In response to the possible piece-mealing of Prey 2 ideas, I wouldn't suspect them being that clever. Moreover, that would be a big heaping pile of [censored] for them to do so. Those were HumanHead's ideas and they deserve to have those exclusive to their masterpiece that is Prey 2.
Prey 1 introduced portal technology before either of Valve's games did. (I respect Valve greatly but HH got the loot first). Prey also made idTech 4 look better than it had ever before and brought about many visually, eye-popping quirks that had not been seen previously.
The point is not so much about idTech 4 or portals, but rather the fact that HUMANHEAD is a very creative, intuitive, and resourceful dev team that know how to make great games and how to make the most out of the technologies that those games utilize and I would like to see more of that.
Prey 2 brought about those innovations (Agile combat, holstering of the gun, and tile-locked, Alien Noire bounty-hunting) and as such they should remain in that title with the possibility to be later expanded upon the much requested Prey 3.