The only thing I'm sure of is that each time I've questioned DSI about the Prophet '08's future, I've been told the instrument is still a big seller. Although the Deepmind 12 may somewhat affect this, I doubt it will be a Prophet '08 killer.
"If it ain't broke don't fix it."
Dave Smith's analog instruments live on the legacy of the P-5. There are a lot of cheaper keyboards out there but none have the DSI sound or reputation. In this day of age I doubt a competitor synth will be able to do to the P-08 what the DX-7 did to the P-5.
So what would DSI be able to make that would make me want to replace my P-08? Probably nothing. If I was buying something in the DSI line, I would probably go with a Pro 2 (which I did) or a P-12. I would do that to compliment my P-08 rather than replace it.
If I am just coming into the analog market, I would want something analog with the most modern features. There is a lot to be said about DCO's over VCO's. SS already discussed it, and I won't repeat it here. If you are a VCO purist, then it is the P-6. That person won't consider a P-08 type synth anyway.
If you're willing to go DCO (which I think is superior to VCO) then an upgraded format of the P-08 is about as good as it gets. So I go with SS's thought of a P-08 Mk II. Stick with the P-08 approach and modernize it with the latest features. If I had my wish list, I would include the on-board effects, high pass or variable filter like on the OB-6, and audio over USB. I would also update the sequencer like on the Pro 2.
Finally, I would put the power transformer into the unit rather than a wall wart. There is something very cheap feeling about a wall wart. I don't use my P-08 for gigs, but if I did, I would be very concerned about the thin wires breaking and having to replace the transformer regularly. If I was still working professionally, this may have been a deal breaker for me. Even without gigging, I don't like moving the P-08 for fear of putting stress on the wall wart wires and connection. That's not something I should have to deal with on a pro level instrument. DSI put internal transformers in the P-12 and Pro 2. The P-08 deserves an internal transformer.
Other than the above, I wouldn't try to improve on an already successful (and potentially classic) product.