Although I think the Abrams M1A2 among the best tanks in the world its competitors; the French Le Clerc, the British Chieftain, Challenger 1 and Challenger and the German Leopard II, the success of the Abrams has left the Army which a few chinks in US Armored Force makeup.
Weaknesses: High Fuel Consumption and lack of air transportability.
The Are working on a light tank presently constructed of Plastic and FBR. As it is a hybrid test vehicle, it mount the 30mm gun from the Warrior IFV.
the final generation of the tank will likely sport FBR and kevlar armor and armament in the 90-105mm range.
The French have been mounting such weaponry of the Panhard series of armored cars for decades.
Likewise the US has a 105mm gunned variant of the successful Stryker IFV.
I do not think that that is air transportable.
Likewise the most successfull Medium tank in History, the British Centurion, has no successor.
Why do we need one or the other?
I owned a boat with a twin trubo British made Perkins Diesel. I was fasr, powerful, econonmical and quiet.
US maritime diesel tend to be on the loud side.
Perkins no longer exports outside world (outside the UK, that is) since they supply the power for the Challenger II, which is as fast and quiet as the Abrams and much more economical to operate.
Am I suggesting this as a replace for the Abram's Turbine Power Plant. No, one does not mess with success.
However I do suggest that light and medium tanks (the former air transportable) be designed using the concepts being pionered by the Brits.
If we look at the scenarios that have cropped up in Iraq, a fast medium tank, economical and well armored and armed with time proven 105mm gun would be more useful in Urban warfare and would be more appropos for the purpsoe of infantry support and, if nothing else, a vehicle that could properly escort the lengthy and vulnerable supply lines that the armored spearheads of Abrams Create.
Perhaps the Styker concept can be diverted or developed for multiple uses-the anti RPG "Rails" would be de rigeur for these tow concept vehicles
"All Enlightenment Gratefully Accepted"