Supposedly, there's also an early implementation of World 3 if I read it correctly? Not entirely sure if this is actually a thing or not though. Besides that, it's mainly World 2-4.
Not quite, i read that as that we should be able to progress the mission selection screen to world 3 after beating the boss, without being able to do anything there. i think that may be bugged however, as I can't move to world three even after killing the boss.
So, what new stuff comes with this update exactly? Aside from the second boss and those drones I mean.
Pretty much just that, this update is the initial release for 2-4, which is just the bossfight, similar to 1-4. the boss has two grabs, one of which we've already seen, and the drones are something that it releases as an attack. No new status effects unfortunately, but the dev has mentioned that they've plans for there to be a total of nearly 20 in the full game, so we can expect another five at least come world 3.
End of Feb update should complete 2-4 by introducing one or more events, likely gameover events in the same vein as trying to fight 1-4 with the stage 2 demon parasite. I believe they're also trying get stage 1 of world 3 done this month as well, because their development plan is to have the game complete up to 3-2, boss included, by the end of april, so i'm guessing:
Feb: 2-4 event(s?), 3-1
Mar: 3-2 stage
Apr: 3-2 boss
After April the paid Ci-en plan will stop, and the dev will do their best to finish up the game within a couple of months. Seems like a pretty good idea to keep them motivated to actually push out a finished game, rather than staying stuck in patreon-style perpetual development hell.
Edit: I derped, dev has outright posted their plan for development up to April. Feb update will only contain a single event for 2-4, though they'll be working on world 3 enemies, March will release 3-1, and April will have a mid-month release containing 3-2 up to but not including the boss.