COH will always be something I come back to every now and again if nothing updates and everything stays the same as it is now, with maybe some small additions here and there.
However, what would get me interested and really keep me playing consistently is knowing there would be consistent new missions, story arcs, task forces, etc. that are come with every update. New power sets would be cool, revamping out-dated old missions/Task Forces is welcomed, and the game's graphics getting an update would be nice, but new content is absolutely essential for me. Continuing the main arc/batallion stuff mainly, but also making brand new arcs for characters of all levels is what I want to see. It can even be with enemies already in the game if that makes it easier... I just want to see more arcs with the quality of some of the later ones we saw. It really felt like the development team was hitting their stride in this regard before the shut down. Obviously it'll be new people handling it, but thus far I have no reason to think the homecoming team won't be able to execute quality stories for us to play.
#2 would be getting rid of those old, cramped, purple cave maps and replacing them with the bigger caves. In all arcs. Except one... just for the heck of it so they're not completely extinct (it'd be a bit cool to still have them for that one mission/whatever).
And I'm mostly a melee toon guy, so any power set additions to Scrappers/Tanks/Brutes/Stalkers would be #3.
Edit: Actually #2 would be adding back in the remainder of the original incarnate tree/continuing with that and releasing them with each update. While I'm sure some people would be against it, I still want to have that all-powerful toon that can wreck multiple AV's at once like what we saw at the beginning of Mender Ramiel's arc. Sure it'd make normal missions trivial... but that's part of the fun. To grow a toon so powerful you can laugh at Maria Jenkins missions solo +4 x8 (which I'm sure some can do already, but still).
Edit 2: Oh, and I second no p2w. Although I'd be fine with requiring a subscription to play the game (not sure I'd recommend it though, but I'd happily pay that).