I think new costumes for holiday events could be a good idea. Not necessarily anything ridiculous, I'm not sure how much time the devs have to work on CoH or how incredibly janky the code base is but if there's even a slight possibility of new clothes, heads, that kind of thing.. I think that's a very good goal to work towards. Generally speaking, when it comes to projects like this I think the same approach servers like TurtleWoW have taken are the best, instead of fundamentally changing the game you create content in the spirit of the old game. You stick to the original ethos, that doesn't mean you can't have new spells, abilities, or missions, it just means that you don't turn the game in to the Ship of Theseus.
If I had some kind of magic device that meant I could generate content I would probably try to add a little something for everyone, new PVE content, a little PVP (not sure if anyone does it here I'm new) some new costume pieces and something for roleplayers. I'm aware super group bases are good venues but I do miss the pubic zones we had in CO. More specifically the plethora of roleplaying locations. There's too many to name. CO right now is flatlining, it might be good to capitalize on these people by making it clear theres content for them. And yes, I know some roleplayers are weird!
On the extreme off chance a curious dev in to roleplay reads this, here's some examples:
CO RP spots ------ > https://steamcommunity.com/sharedfiles/filedetails/?id=566181114