If there's to be a new DSI flagship, then that's the most obvious blend: the P12-P6 masterpiece, which would certainly cross the $3,000 mark.
I'm not sure whether that would be a realistic scenario. The design philosphy with regard to DSI's whole catalog has always been to develop instruments of which each covers a specific set of options and sound generation tools without too many overlaps between the single devices. And while there have been groups of instruments like the Prophet '08, Mopho, and Tetra for example, or the Evolver line, there has never really been an instrument that does it all in one package. In that sense, I'd expect that the closest you'll get to a P12-P6 masterpiece in the long run is in fact going to be a combination of a Prophet 12 and a Prophet-6, or two of the latter for the sake of an equal voice number.
I also don't think that DSI is a company that has one flagship. At least with regard to polyphonic keyboard synthesizers I currently see them offering three flagships: the Prophet 12, the Prophet-6, and the OB-6.
Beyond speculating about specific designs, I think it's safe to assume that the following instruments won't happen (anytime soon):
- a new drum machine
- a monophonic version of either the Prophet-6 or the OB-6
- a bigger version of either the Prophet-6 or the OB-6
- a desktop version of the Pro 2
- just about any combination of the above in the manner of just putting two or more instruments into one box
That said, I'd expect something that differs substantially from synths like the Prophet 12 and a classic analog synth like the Prophet-6 or the OB-6. And while the latter two are gorgeous synths, one wouldn't go too far by describing them as the most conservative designs that DSI have ever developed. I don't mean that in a derogatory way, but very much in the sense of Dave saying "it's 1979 again." Taking into account that the (re-)development of the classic analog polysynth design has kept DSI busy from the latter half of 2014 up to the release of the OB-6 (besides the occasional firmware maintenance of course), I would strongly assume that the odds are in favor of a different direction now.