1. AliensRL isn't done yet.
2. No guarantee Kornel would release the source even then, and almost certainly not now (unless of course someone corrects me, but I doubt it ;) ).
3. Unless Kornel dies or suffers a horrible setback, it's probably going to stay his baby.
4. Suggestions for a sequel are only really worthwhile IMO if someone's stepping up to the plate and making it; dreams are nice and all, but unless someone is inspired enough to put in some work that's all they can be. Now, maybe someone can come up with a suggestion that provides this kind of inspiration, but how often does that happen? Player suggestions make it into independent games, yes, but still not a lot, and there's a lot of chance involved when it comes to someone dedicating their time and energy to something that isn't guaranteed to be profitable. Not that it *doesn't* happen (for which I am grateful :) ) but it doesn't necessarily happen often, and for every independent project/person that succeeds there's at least three that fail (if not more).
5. Your suggestions already are on their way to making this game a lot of work. Net play, for example, isn't FWIH easy to put together, and there's AI for teammates, enemies, civilians/survivors... it sounds neat, but it's non-trivial to put together (all worthwhile games are non-trivial, obviously, but the work part of making a game is a key part of why a fair amount of people stop working...). As approximated in 4, the dream is neat, and I might like to play this game too, but unless someone is willing to work hard (I don't have the coding knowledge or, I suspect, the disposition to do this) at it it's just not gonna happen.
...You can call me Buzzkill if you'd like. :P