Is the FX revolution fizzling?

That doesn't make sense. The viewfinder is not affected by sensor size, it's optical, so DX/FX is irrelevant there. As for frames per second, also not a sensor size issue, it's a data issue. The D4 is up to 11 frames per second as a FF camera, but it's also substantially less data than the D800. There are trade-offs to be made there, at least today, but that will change.