Its being tried in Sacramento already, and its bound to happen in other places.
In markets like LA and across the South, Southwest and West, I wouldn't be surprised to see more rhythmic variations of 90s hits then straight up all 90s hits stations. I think a 'classic hip hop & r&b' format may very well be the 'jammin' oldies' of the next decade. Of course, that means that all but a few well executed stations are destined to fail.