This is just an idea but there could be a final boss for Gen Zero because the ending is kind of anticlimactic. my idea is that FINX is about to launch a missile containing a ton of robots from FOA 53 onto the Swedish mainland In an effort to take over the rest of Sweden. the reason why FOA 53 is that there is that big walled area and inside is what looks like a missile silo. there could be a Reaper guarding the launch site but instead of shield generators on the Reaper, there could be shield pylons on the walls that you have to destroy, and pretty much if you kill the Reaper and stop the missile from launching in a set amount of time, you get a good ending where the world is saved and if not you get a bad ending.
A boss fight in that Arena, yes.
An end for GZ, no.
GZ has to live on.