The plans aren’t necessarily all in one location, they’re kinda scattered about (and as time goes by some of them get replaced with slightly better ideas, nothing is truely “solid” until it actually gets into the game, just more or less widely canonized). To sum it up briefly:
Blob - Not really gonna happen, as noted in this thread. That said zombies aren’t exactly the most intelligent of creatures, so you might be able to fool some on a local scale. Maybe eventually have a sub-branch of the slime mutation set that lets you get into a position where you could possibly “hijack” a small number of zeds or blobs (though it would be useless against the faction at large).
Mycus - Already in game. Open up the fungal mutation and you’ll join them (and as we get around to a changing world and more fungal content this will expand more).
Triffids - Eventual goal is to fight your way to a triffid heart and then convince it that you aren’t going to bend to its will. At that point it might be willing to give you quests that could allow you to win its trust (and possibly some other hearts’ as well, but not all of them, they aren’t exactly the most trusting or friendly bunch); at least up until the point where it backstabs you. Triffid hearts are eventually planned to be much closer to NPC type characters than monsters that just happen to be hostile at the start, (though hopefully much more stable and a bit more alien than our current NPC’s! :P).
Horrors - Not gonna happen. Might end up with some horrors of the “follow the relic” type that you could harness by stealing their artifact, but you aren’t going to be befriending amigara horrors anytime soon and each one is its own little group.
Mi-go - Don’t get slaughtered when their invasion comes. Present yourself as a willing second-class citizen at one of their outposts and convince them that you can stand on your own without being a slave (and don’t let them find out you’ve murdered any Mi-go’s, that’s a good ticket to an execution).
Shadows - Not gonna happen, they’re just too strange for anyone to reason with now, be they denizen or earthling.
And that’s about it for the moment.