After giving up waiting, I changed allegiances. 
But I still use Groove Agent for generating ideas, which I may then convert to MIDI for use in another product (with much better samples).
However GA 3 was far too buggy with fills and the like being mis-triggered. Also after extensively working on one song in the first release of GA3, the second release completely screwed up a lot of hard work on automation. That really put me off trying to do tricks in GA3.
So I’d be interested in GA 4, with a good upgrade price for existing users. But You need to get you software testing sorted. 
And ensure that you maintain the generate MIDI function. Larger drum kits with more toms? And Don’t forget the roto toms!
And what about Virtual Bassist as well? Another great product that has been languishing. Could the two be combined, to create a general Rhythm section? That would be a great product.
I’m not to worried about Virtual Guitarist, now I can actually play some guitar!