There is no technical reason why AOS4 can't run on the Pegasos, I'm sure if Genesi get there way it will run on it (They like lots of OS's on their little board).
The only thing stoping AOS4 on the Pegasos is Hyperion, and thier politics.
Mark my words, a few weeks after AOS4 is released, some clever hacker (the Amiga community used to have lots of these) will get it running on his/her Pegasos... :-o