I seriously hope they don't add any new materials/currencies in the coming expansions, because we're already overloaded. Seriously, there are so many, and half of them end up being practically worthless because you have so much. Let's recap all the currencies (by currency, I mean anything that is used to purchase/upgrade items):
Glimmer
Vanguard Marks
Vanguard Commendations
Crucible Marks
Crucible Commendations
Spinmetal
Helium Filaments
Spirit Bloom
Relic Iron
Weapon Parts
Sapphire Wire
Plasteel Plating
Hadronic Essence
Ascendant Energy
Ascendant Shards
Radiant Energy
Radiant Shards
Strange Coins
Motes of Light
Exotic Shards
That's 20 different currencies (18 if you count the three different class materials as one). No wonder the economy is so screwy and people end up getting worthless stuff they don't need from things like Raids and nightfalls. There's so many that you can't actually carry every different sort in your inventory at once.
House of Wolves really, really shouldn't add more. In fact, I think they should overhaul the system to reduce the number. Or, at the very least, introduce some kind of 'stock exchange' where you can exchange materials for other materials, perhaps based off some kind of semi-random (Bungie do love their RNG), fluctuating exchange rate.
Edit:
For those of you saying that upgrade materials aren't curreny; you are right in the strict defniniton of the term with regards to real life. But in the game, they function in the exact same way. You still buy things with them (upgrades). The fact that they are not called 'coins' or 'marks' or whatever changes nothing. You use them to make purchases, therefore they fulfill the same function as a currency.
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Half of those are upgrading materials , not currencies