[SPOILERS] Ending discussion

[GrAVit]

Yeah, it's Simon #4, since he's like "Did we make it?" when he wakes up in the pilot seat in the ARK. That would be Simon's immediate reaction to making it to the ARK. The game just decided to stick with Simon #3 so you'll see the depressing end of him, and then go to #4 after the credits for a happy end, sort of.

If there ever will be a DLC about SOMA, I'm thinking it'll be a prequel, since stuff started going bad long before Simon #2 woke up. Many things went unanswered, such as how Reed ended up in the pilot seat in Upsilon, that Simon #2 later "possesses".
Though if there's going to be a sequel DLC, it's probably got something to do with the ARK or a new protagonist completely, because sticking with Simon #2 would make your choice (if you killed him) non-canon and meaningless. Killing or sparing the WAU would also probably affect the DLC a lot and one of the choices would have to be canon, so I doubt it'll take place in Pathos-II if it's a sequel.