So I've just found out about all this and went reading into it. One thing that I keep seeing people say is "Destiny Like"... I'm curious, how would you make an MMO with a persistent world feel survival horror at its core? Unless there was a brutal Permadeath mechanic in which if your marine dies, you end up having to create a new rookie and work your way back up* (Thus making it actually worth being careful and thinking, unlike Destiny. But this would require balance and specific blocks like "Group Missions are Not PK" for example)). I also can't help but think about a core mechanic of MMOs and persistent worlds, which is skill systems and looting. I feel you'll need classes for that. Medical, Combat Engineering, Systems Technician, Pilot, so on.
**Or like how Escape From Tarkov Handles it. Main Character with loot and skills, and a timeout when killed Secondary "Scavver".
Course, all we can do is speculate right now. But I'm trying to figure out in my head how it would even work. Not to mention you'd need a damn good story and consistent chapter updates for the community (Ah-la Star Trek Online. It just won't die and still has a thriving community. Plus the main storyline is actually decent and replayable to an extent, for MMO standards.). Also, no Loot Boxes... And if you gotta have microtransaction, make sure it's cosmetics only, no P2W shit.