This list is gonna contain ideas and fixes from multiple users that are on the forums, of course they may be not original, but I am still going to try to source back to whoever is asking recently while adding my own ideas related to it separately (like 1a, 2a, etc. ie):
1) Telementry Data to be used for something different, one suggests for it to be re-rolling perks on a owned weapon. Post: https://www.bungie.net/en/Forums/Post/255124575?sort=0&page=0
1a) I think that the Telementry data should cost 10 to 20 to re-roll a perk on a weapon (10 on Primary, 15 on Energy, and 20 on Heavy). The data should also be used to increase infusion cap by 1 season at 250 telementry data on any legendary weapon except Pinnacles.
2) Sparrow Racing League (SRL) to be brought back as a way to relax since it is racing and not shooting in a way. Post: https://www.bungie.net/en/Forums/Post/257777362?sort=0&page=0
2a) There should be 2 kinds of SRL while containing a Tutorial version of it to unlock more functions of the Sparrow in open world. First, the Tutorial will introduce drifting and new functions used in SRL while showing how to use a new Sparrow attack to be used in open world. This will enable the user to drive Sparrows faster than 180 speed in open world up to 210 speed. Second, the causal version of SRL will be at 180 speed always with unlimited energy, the kind seen in D1, rewards will drop new armor, sparrows, and weapons that can be used on the sparrow in Open world (Sidearms, Hand Cannons, SMGs, Swords, and possibly Bows?). Finally the Third, Competitive SRL will be 210 Speed always, can only use Thusters for more speed at a cost of a slow debuff for 1 second up to 3 seconds (unless on a ramp/in air), moving side to side up to 3 times before refresh on a booster. The rewards on competitive SRL are Armor with +65 stat, curated version of the weapons, AND a specific sparrow with new perks to be used in Open World. Amanda Holliday will have a quest in the Tower to introduce you to SRL and IS the only source for upgrading the speed of the sparrow and to buy sparrow mods for open world and SRL. This will give us a reason to visit Amanda Holliday more often than exotic quests.
3) A dungeon that would feature a possible return of SIVA that the Lord Saladin wants us to help investigate, loot you can receive will be SIVA themed weapons. Sadly I cannot find the post again.
3a) My idea about this was that the quest must be obtained by doing 1 Iron Banner match, then you will be set on either PvE or PvP of your choice at start, but will slowly shift to PvE unless you already selected PvE. Next, it'll have you investigate the area nearest to Plaguelands in the Cosmodrone which will be on the map as a Dungeon. After first completion, that dungeon will stay unlocked for all players who done the quest with Lord Saladin being one talking by comms during Iron Banner event. If the event isn't up, then Tyra Karn will be on the comms with info from Lord Saladin. This Dungeon will be Free for All players since this comes from a event for all players.
4) Wes talking about all the QoL things that bungie can do. Post: https://www.bungie.net/en/Forums/Post/254851170?page=0&sort=0&showBanned=0&path=0
5) The Prophecy dungeon should contain Trials of the Nine weapons while making the current weapon rewards be in World Loot. Post: https://www.bungie.net/en/Forums/Post/257785199?sort=0&page=0
5a) Trials of the Nine armor is in the Prophecy dungeon, so this makes sense and I personally don't mind weapons this old be brought back as long it has random new rolls we can play with that we haven't played on the weapon yet.
6) More quests that doesn't cost silver like the Adored and the 3 activity quests. Post: https://www.bungie.net/en/Forums/Post/257662543?sort=0&page=0
6a) This makes more sense, after the big vaulting... It was empty with nearly nothing to do except try to get to 1250, plus it gives us players something to be distracted on while we wait for more areas to be done like whole Cosmodrone. Since Rocketyard, The Grottos, King's Watch, and The Blast are areas I eagerly await.
7) Factions in general. Post: https://www.bungie.net/en/Forums/Post/257771311?sort=0&page=0
7a) There was a comment on the topic by Starstriker7 that said the choice should be account based and the weapons between each faction should be the same, but with different decal to represent their faction. Aka the smartest way I heard that can bring back Factions nicely, this helps distracts us more on something.
8) Buffing older exotics for players to try out. Post: https://www.bungie.net/en/Forums/Post/255269446?sort=0&page=0
8a) On Legend of Acrius, the Long March perk is something I like using in PvP of course and if the weapon was a Energy, then I would favor Surrounded perk more.
9) Armsday should be reintroduced. Post: https://www.bungie.net/en/Forums/Post/252622746?sort=0&page=0
9a) An old post, but the amount of vote accumulated speaks for itself, the weapons we should get from Armsday is D2 Y1 or even D1 Y1 Armsday weapons, but with random rolls with Wellspring and Surplus included.
10) A comment from the SRL post, which states that Combined Arms from D1 should be added.
10a) This mode was my favorite and can help deal with stasis much easier than maps with less space to work with. The mode can also be a Iron Banner mode that has the same function as normal Iron Banner, but on the bigger map with vehicles and the Iron Lord's Battleaxe which gives buffs to take on gunfire easily with the weapon.
11) A post with a poll suggesting to add more strikes. Post: https://www.bungie.net/en/Forums/Post/257702452?sort=0&page=0
11a) There was a Strike missing from the D2 Cosmodrone, a variant the Devils' Lair strike. A strike where you start at the Divide in front of the entrance to the Rocketyard. Of course the Rocketyard has yet to be release, but I like to believe this will be released along with King's Watch soon. Although I do not remember any other strike from D1 Y1 aside from Devils' Lair... So I don't remember the D1 strike at the far-left side of the D1 Cosmodrone map.
12) A concern that needs to be addressed, about Iron Banner's upcoming loot. Post(s) and Video: https://www.bungie.net/en/Forums/Post/257788415?sort=0&page=0 https://www.bungie.net/en/Forums/Post/257782030?sort=0&page=0
https://www.youtube.com/watch?v=bz2Msv9c61U
12a) I actually don't mind D1 loot entering D2 lootpool since I wasn't able to go far in D1 with a PS3 back in those days, so this can bring immense interest to those who never got to use the weapon and nostalgia to those who have used it before. There is no need to be afraid to reprise weapons as long it has new perks on it or that it never entered D2 before. I welcome epic looking armor and weapons to toy with that enters D2, even if it was from D1.
13) Fixing wording of Exotic's Catalyst requirements to apply the masterwork. Post: https://www.bungie.net/en/Forums/Post/257376482?sort=0&page=0
13a) A most likely easy fix is to adjust certain Exotic weapons to match the Catalyst's masterwork requirements. As for armor, it is needed to specify about it since there were people who were fooled by Mask of the Quiet One's text on stream to be disappointed about how much health one gets at critical health.
14) Iron Banner UI update, this is something some people addressed, but not enough. Cannot find the posts tho since they are pretty old...
14a) No seriously, the Iron Banner UI needs an update similar to Crucible a bit.
15) Possible issue, Hawthorne speaking the same thing ever since Red War. Post: https://www.bungie.net/en/Forums/Post/257620149?sort=0&page=0
15a) New Lights that entered after Beyond Light or that did not complete the Red War campaign will be confused ever since the giant vault. Text should suggest helping out in the solar system and then second half of red war text is there, easy fix. Another easier fix is setting up a offline version of Destiny 2 but has the 3 campaigns there and will only load the data to indicate that they did it to the online Destiny 2, of course New Lights that entered Destiny 2 after Beyond Light need to pay for this.
16) Someone missing out Red War (F), but the fix I mentioned is at 15a. Post: https://www.bungie.net/en/Forums/Post/257779364?sort=0&page=0
17) Someone suggesting Ascendant Shards in Crucible. Post: https://www.bungie.net/en/Forums/Post/257779364?sort=0&page=0
17a) Even though I have really no knowledge of how balanced the loot is, I can agree with this. This change would make me grind for max rank.
18) A suggestion I have when the Rocketyard, The Grottos, The Blast, and King's Watch come out to be available, make sure it is an Adventure we do to unlock the areas. Nessus and Cosmodrone are feeling a tad empty without Adventures or quests within these areas, so if we have quests that go up because of lore or to unlock a new area to make things more lively for both DLC and Free to Plays? Then HANDS DOWN I am in for this! Plus this gives Shaw more lore that can makes us like him instead of wanting to punch his face.
There is a lot of things the community can do that can help Bungie be guided the right way, but outright complaining on everything or thinking Bungie has done nothing wrong doesn't solve it. I believe with enough people wanting change for the better to express their concerns, then it will be done right.
Edit: There is now priority list, I have a comment below of reasoning why to with a priority thing going on. However, the Priority list is gonna be below on 1 as Highest to 9 as Lowest :
1) 12
2) 6
3) 5
4) 2*, 7, 9, 10
5) 3, 11, 18
6) 4, 17
7) 8
8) 13, 14, 15, 16
9) 1
* = Can be considered number 1 alongside 12 given it is introducing more loot
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TDT Video about SRL and thinks it's the perfect time to reintroduce it: https://www.youtube.com/watch?v=i-QUC2PaQpk