I think we need a new light tank like a modern Sheridan, fast with band tracks, possibly a hybrid drive, amphibious, and a 30mm main gun. It could fire HE rounds to support troops, or the same DU rounds as the A-10 at armored vehicles.
Making the T-34 relevant again...battlefield dominance doesn't mean just good enough.
The Abrams was a game changer because it made everything else obsolete and allowed us to change how the game was played; we were no longer planning to just stop the Soviets from pushing to the sea...we were going to Moscow and they couldn't stop us. The 30 on the A-10 works because it doesn't fire one round at a time.