I think I'd like to see this but implemented in a different way. I'd prefer the mix side of things to handled by rack devices so you can use a dedicated RE to crossfade and so on. For the audio side I'd like the sequencer audio tracks to have pitch/tempo control like a turntable. This would allow you to do chops and edits on an audio track and play it back as if it were on a turntable without having to bounce it to WAV. It would make doing reedits very simple.
This could even be applied to MIDI tracks for tempo control. You'd have to lock the pitch of any matching audio files so everything stayed in tune but it would be a great tool for live sets as you get the best if DJing with the option to do tweaks on the MIDI info.