Its a bit out there, but I have an idea for a special server which is Romans vs Teutons vs Gauls. You can still have separate alliances, but only member of your tribe can join your alliance. (This allows for competent leadership to still be a thing).
If you used victory points (as in special servers) you could just have whichever tribe gets the most. Honestly, it would just be cool to see all three tribes compete against each other. You'd maybe have to cap tribes at 40% of server players just to make sure that it doesn't become too unbalanced but I'm sure it could be done.
Would love to know what others think.