I actually have to suggestions.
#1: I think there should be a all tank mode, where you have to take the other enemy base. A great way would one team and base on each side of the water connected by the bridge.
#2: I think there should be anti-aircraft guns at like each corner of the base. How it would work is: When you're shot down you can choose tank,airplane or gun. The gun would be anti-aircraft and have limited ammo. Once the gun was out of ammo the player would be immediately put back into a airplane.

I hope my suggestions might help, this is just what I think would be nice. I hope other people post their suggestions.

I've always liked the idea of a tank game, although I don't see the point of doing it on the bridge. A choke point like that would be impossible to cross without air support.

It might be a fun game mode planes started at each the bases, and you had to get a walking soldier into the building on the end of the bridge, and keep him safe for a length of time. If he died, the timer reset to 0. You could use planes, tanks, or even other walkers to attack and defend him.

As for the AA guns, I've always been against that. It would be next to impossible to NOT get shot down by a stationary target. It's really fairly easy to aim a tank at a plane (Think of the ratio of shots you've hit planes with, and shots you've taken. It's really pretty high), if you had a stationary machine gun that can pump round after round of ammo into the air, think how impossible it would be to come in and bomb without sneaking.

Actually, that might be a fun new game mode, too. Make it a separate game that you can't play right down the middle. That could actually be pretty cool, but it shouldn't replace the originl BTB.