Since we technically paid for guns (I know we don't onw them, Bungie) like Pluperfect and Patron of Lost Causes, but never got the chance to use those guns to a good extent of their lifetime (they got basically sunset after Season of Arrival), I think we should be able to get them again from open world loot drops or activities.
More guns mean more selection of killing tools and since the guns are still in the game, it should be not that hard to just enable infusion for newly dropped rolls of those.
For clearance, I am not speaking of guns that were pinnacle guns in pvp/pve/gambit. Only the Season Pass exclusive gear.