I don't see how they can do anything other than cosmetics and maybe refresh a weapon pool as craftable since they just found out about this last month.
Here's my guesses for what we might get:
A new Moments of Triumph armor set tied to a set of objectives with a corresponding title.
VoG or Garden gets craftable weapons+updated perks.
I guess they waited until they had a better idea of what they could offer over the longer season and the day before the next dlc is about as long as you could wait really.