Yes, it would be interesting and I (and games) have imagined quite a lot of "what-if" battles between various
characters.
Like the game Mobile Suit Gundam: Encounters in Space does have a "What-If" level for the Battle of Solomon
where, rather than battle Dozle Zabi in the Big Zam like the anime (and normal game play) does, Amuro ends up
encountering Anavel Gato (in a custom Rick Dom), Carius (in a Zaku II), and Kelly Layzner (in a Bigro) and essentially
ending in a stalemate. Even later, during the Battle of A Baoa Qu, there is a "what-if" battle where Amuro
encounters Gato in his custom Gelgoog as well.
It would also be interesting to see more characters that are more-or-less just from side stories, novels, etc be used
more too (like Johnny Ridden, Shin Matsunaga, Yu Kajima, and others).
Some I've usually been interested in...
Amuro Ray vs. Anavel Gato (because of the game)
Char Aznable vs. Johnny Ridden (given the constant confusion between the 2 because they both like red)
Shiro Amada vs. Yu Kajima
Yu Kajima vs. Kou Uraki
Shiro Amada vs. Kou Uraki
Kamille Bidan vs. Judau Ashta
Paptimus Scirocco vs. Judau Ashta
Seabook Arno vs. Uso Eving
Athrun Zala vs. Yzak Joule
etc
etc