The Sentinel idea has been done similarly by another company already. Multiple Sentinel parts with X-Men characters on top of the remains.
What I would like is for them to continue but using different bad guys. The Brood Vs Nightcrawler/Gambit, Calysto Vs Storm, Mojo Vs Longshot/Dazzler, Juggs/Black Tom Vs Rogue, Emma/Beast Vs Ord (Astonishing bad guy), Cable Vs Stryfe...I could go on and on. My only rules would be:
1. Keep the matchups relevant. Everyone within the X-men has a certain bad guy that is their nemesis. We have seen it with Wolverine Vs Sabertooth, you see it in the example above Calysto Vs Storm. I paired up Juggs Vs Rouge because she has the power to at least take the beating from such a character. Keep the X-Men fights relevant to their nemesis or a famous encounter from the comics.
2. No Wolverine. At least for a while. The next Wolverine diorama I would like to see in the far future is Wolverine/Kitty Pryde Vs Danger. That gives us Wolvie in the Astonishing costume we have not seen before at least. Other options are Wolvie Vs Wendigo with the old school first appearance costume. Last but not least, Wolverine Vs Omega Red with Wolvie fighting Red in the snow with the torn costume. Basically, we get Wolvie but in different ways than we have seen him before. Otherwise leave him alone for a while.
3. Give me some surprises. Mojo Vs Longshot/Dazzler would be unexpected but very welcome. I know a lot of folks don't read the comics and want their popular characters, but give comics fans some of the less known characters too. Cannonball could be a cool one if done properly. Multiple Man is another character that lends itself for a creative diorama. Keep the creativity alive with the Vs dioramas.