Re: Who should be the villain in an Avengers sequel? (Poll)
The words final and reboot aren't being used in the context you're claiming they are. Someone saying there will be a final showdown with Thanos is not someone saying it will be the final Avengers movie; the mention of rebooting was in regards to "one-shot" franchises lending themselves to reboots more easily.
None of the posts even remotely suggest that there will be no more Avengers movies or an immediate reboot after Avengers 3. A trilogy does not mean "no more movies", as we've seen many many times in the past decade. It means "we wrap up some overarching story points, and give some closure". That doesn't preclude an Avengers 4. It does, however, give them an out if RDJ and Hems and Evans all decide to move on (likely).
Anyway, back to villains.