MBT obsolete? I don't think so. The current expereince in Iraq shows that an enemy loaded with RPGs in an urban environment is going to need a heavily armored adversary. Bradleys and even Strykers are vulnerable. Fuggedabout Humvees.
Special situations call for variants on proven forms. Look at all the guises the Sherman took on in WWII. Look at 'Hobo's Funnies' in the WWII Brit Army.
Maybe what will be developed will be a specialist urban warfare MBT- something like an Abrams or Merkava with a shorter gun to be more manuverable in tighter older cities, and firing a flechette beehive round
( with more reliability than the old Sheridan ). With some auxiliary weapons like 40 MM mortar or that new intelligent 23mm 'machinegun' weapon system we are developing, such an MBT would be the E ticket to ride in urban battle or possibly close-up infantry support elsewhere.
Ultimate answer is to ask the Israelis if they have any plans to give up on Merkavas. 'Nuff said.