I just want to see the Superman /Flash Duo that Gon & Killua become when they are older
Didn't Gon permanently lose his ability to use Nen? He might be out of the story permanently breh.
If it was another writer I'd expect Gon to regain his powers somehow, but Togashi is the type of person that's perfectly fine with switching protagonists. Plus, even if he had is powers, Gon doesn't really have a motivation to be a hunter any more.
His whole reason for becoming a Hunter was to find his dad, which he did. If Gon came back I'm not even sure what he would be hunting for.