Cherenkov radiation is a proof, that FTL is possible. We just cannot accelerate enough. However, «burps» from blackholes are proof that blackholes can do that. To achieve singularity, outer layer of blackhole core must spin at a FTL speed anyway.

Cherenkov radiation shows that FTL is possible in a medium where light is slowed down below a the maximum possible speed allowed by special relativity. It does not show that FTL as usually understood is possible.