See I think the Prophet line CAN be expanded but the problem is it's not. Before Sequential took the Prophet and expanded it with a bunch of incarnations...the Prophet 10, Prophet VS, Prophet 2000 etc...so why not now?
But DSI did release the Prophet '08, the Prophet 12, and the Prophet-6, which are all very different. So it's not really that we haven't seen any Prophet incarnations in the more recent past. Even the Poly Evolver and the MEK have once been advertised (around 2006) as continuing the story of the Prophet-5 and the Pro-One.
Like I posted above why not 2 synth engines on one synth? Why not 4? Why not an analog/sampler hybrid? Why not an FM or VS based Prophet?
While some of that would probably be possible, it has never been part of DSI's philosophy to design one synth that can do it all. Even the ARP Quadra you were referring to earlier wasn't that kind of synth. In fact, it wasn't even a true polyphonic synth like all the Prophets are, since it utilized divide down technology to achieve polyphony like organs, the many string machines, and the Polymoog. Its synth engine was also not immensely powerful. But even if you upgrade all that to today's standards and expectations, you'd probably end up with a quite expensive piece of gear. So from that perspective I do get it if DSI suggests (by their range of products) to simply get the Prophet 12, the Prophet-6, an Evolver, and a Prophet '08 if you want all these aspects combined for example. Of course that's still very different from having it all combined under one roof so to speak. But I assume that if you'd combine 3-4 different engines you might also have to pay at least 2-3 times the price you'd usually pay for one rather specialized synth, especially if analog is involved all along the signal path. And the other risk is that you can also overload a synth's engine, especially if you are forced to rely too much on menu diving in the end.
The OB6 to me was absolutely disappointing because it was laziness instead of innovation. I mean it didn't even increase the polyphony from their last synth that had just came out! Come on. It's has nothing to do with having more features..it has to do with having each instrument have it's own identity and I really hope it's not a sign of things to come. I don't need another Prophet 6 with a negligibly different sound. I want something different.
While the OB-6 was obviously not for you, it was never advertised as the most innovative synth. It was mostly based on a rather spontaneous idea by Dave and Tom. By following through with their idea, they've made the first analog polyphonic Oberheim synth available since the 1980s. And for many players that was already enough, as it introduced variety to the poly synth market and something people were lusting after for years. And that's okay too.
Plus: That each DSI instrument is supposed to have its own identity is no sign of things to come, it has always been that way, ever since the Evolver was introduced. Also: Isn't it in general one instrument's identity that attracts us to a specific synth, a guitar, or whatever instrument?