Game wise:
New content in all regards - missions, Task Forces, ATs, Power Sets/proliferation, enhancements, inspirations
New zone events would be nice. Possibly events with over-world implications, either positive or negative.
Also my 2 long time requests: Hats for Monstrous Heads and a proper overalls costume piece!
In general:
What I would -not- like to see is micro-transactions of any kind. I have no issue paying a reasonable monthly sub but being nickle and dimed for a fifteen year old game would be a major turn off - especially since a lot of the QoL improvements were done voluntarily after sunset.
Overall, transparency and interaction with the player base should be paramount. You have loyal (waited 7 years to play again!) fans/customers/players and will continue to keep them with honesty and support.
until