If I am understanding correctly, overbridge is something like the "total integration" feature of the Virus TI line.
There are a number of issues that tend to emerge with this approach (like the synth vendor's ability or willingness to keep up with changes to the host operating systems version over time), dealing with USB latency on high voice counts and other integration woes, to the point that support for the integration costs the vendor more than the support for the hardware.. which is one reason I believe that more products don't do this.
For me, the biggest problem with audio over USB is that it never sounds as good or as alive as just using analog outs going into the converters of a good audio interface on the same synth. To my ears it just seems to suck the life out of the signal (and I've seen reviewers say the same thing, at least about the Virus).
I totally get the convenience factor of USB integration... and to some extent maybe the plug-out model of the Roland System 8 is a good approach to integration for a virtual analog synth that solves some of these problems.... But Sequential/Oberheim synths are best known for their analog sound and how they function as stand alone instruments, so huge investments in DAW integration might not make that much sense for them from a business model perspective.
Most of the time, working with analog gear and DAW integration is an inherent pain in the ass compared to the convenience of VSTs, and I totally respect that some vendors seek to bridge that gap with proprietary solution, but I don't think it is every vendor's responsibility to integrate with every other vendor's proprietary solution. MIDI is kind of a lowest common denominator but it still remains the most universal method of interoperability.
I didn't understand the challenge around having a MIDI and an audio track. If any DAW doesn't give both options to do either that, or have an integrated "external instrument" track, I would definitely seek out another DAW, both Ableton and Cubase do this no problem.