I have had a support response from Steinberg’s Miguel Morales. There is no provision that I can see to correspond further. The ticket now says (optimistically) “solved”…
"I think the Problem is actually that Cubase Pro 9 it is not compatible whit Virtual Guitarist at all. Unfortunately, the development of Virtual Guitarist and Bassist has been discontinued. As a result, maintenance updates or installation kits for current operating systems are no longer available.
We don’t recommend to use the bridge solutions because we can’t guarantee its properly behavior.
You can use your Cubase Pro 8.5 to work with 32Bits based Plug-Ins. You don’t need a new license to do so. Your Cubase Pro 9 licences allows you to open all lower version from the generation 9 and older. "
…Since people have reported that VGTR works in C9, this is clearly not the whole truth, it’s a cop out. But it doesn’t look hopeful for a solution. I am ok in that I still have 8.5 installed and indeed SX3 to fall back on for access to much older work, others moving from C9 to 9.5 must expect problems.
I have been in this game for 42 years as a professional and seeing long term backward compatibility treated in such cavalier way pisses me off greatly. If want to access projects from even 5 years ago, I have to cross-stitch and patch across programs.
Final note to end rant. The moral is, don’t trust your Steinberg software licenses to last into the future, even though you paid for the instruments. This is the only software I own that has been treated like this.