I can certainly agree with you that formats have to evolve, or they'll go away, just like standards and beautiful music. Smooth jazz seems to be going that way, too. Classical would probably be almost gone, too, if colleges and universities didn't mandate their stations play it in at least a few dayparts. My point was that classic hip-hop isn't likely to be the next evolution of urban AC because there is likely to always be a demand for African American females from advertisers. Classic hip-hop is unlikely to replace urban AC as the best, and most efficient, way of reaching African American females.
If classic hip-hop proves to have legs, I'm not sure if it's the next incarnation of urban oldies or if it's something new, like classic rock was in the mid-80's. Classic rock arose out of rock programmers' frustrations of having to decide how much pop they wanted to play. Rock product wasn't strong enough to sustain a current product, and programmers were having to worry about whether to add Michael Jackson and Lionel Richie to their rotations. The solution some of them found to this frustration was to reach into the vast collection of rock gold that was available and largely not being played. The approach worked quite well, and other struggling stations in the market would often just decide to grab the gold and eschew the current product the rock station was continuing to play. The result was a brand new format. Of course, hip-hop today has a lot more quality product than rock did 30 years ago, but we could have a similar situation unfolding. We'll just have to wait and see.
As for the difference between urban AC and urban oldies, urban AC is usually current and recurrent focused with popular gold tracks still making up a good portion of the airplay while urban oldies is gold. Urban AC is also tested on females only while urban oldies is tested on both males and females. Having never programmed an urban station, I can't tell you the specific ratios of current-to-gold on urban AC nor can I tell you exactly what percentage of the test group for urban oldies is male (though I understand it uses more females than males in testing).