Ooooooooohhhhh Good question Spud!
I don't know all the ins and outs of his contract, but I do believe he has fufilled his album obligation to Capitol. HOWEVER...
I do know Garth has said as long as he makes music he hopes to be making it under the Capitol umbrella. His mom recorded for Capitol, and he's always spoke highly of how they treated her.
However... he said he'd never step foot in the Ryman too... things change. VERY interesting thought! Maybe you should suggest it to the Gman?