Some Thoughts on S3
At this point, we don't really know what Bungie is planning for S3 other than an increased focus on PvE and PvPvE, but I wanted to outline some things I think I'd like to see heading into the future of Marathon:
Valuables / Salvage Revamp
Obviously, this is a bit of an ask but for me the fact that I'm still looking for the same salvage and finding the same valuables that I was finding in S1 to be a bit boring. To be clear, I'm not saying a brand new system, but maybe a handful of new mats for each rarity would be cool and at least be a relatively cheap way to provide some novelty / lore.
Contracts
At this point, voice-acted cutscenes are probably a cost too high so why not dive into more of the weirder, ARG-style stuff Bungie knocks out of the park each time? I think we just need more writing in general -- doesn't matter if its voiced. The way the contracts unlock or play in-game is less important to me than what they unlock / reveal about the world.
Solo Support
Treat Solo like the VIP experience that players want it to be. Vault Breaker's increased crit damage for solos was a really good step in the right direction for a solo PvE experience. More stuff like that, among others that make the solo experience an enjoyable one / more unique than the standard trios mode would be welcome.
Ranked
At this point, Ranked needs to be entirely rethought. I think instead of making it a separate mode, having it be something like how the Codex Titles work with objectives and achievements could be cool. Something that rewards an understanding of the entirety of Marathon - not just PVP. Let Cryo be the premier PvP experience.
Cryo Archive
Speaking of Cryo, I think having the big bad map be more locked down could be interesting. Keeping teams in their spawns for longer, having more prerequisites to get out / less prerequisites for unlocking vaults, and just more direct Faction representation in what is on the ship would make it feel less like a huge slog and more like the "exploring the truth of Tau-Ceti and the UESC" goal Bungie stated to have prior to launch.
Anyway, these are just some ideas I've been mulling over lately. Interested to hear what other folks are thinking.