I thing we at CJE may have sold to end users more than 50% of all viewfinders sold. We have also supplied quite a few AGP cards as upgrades. Fewer than 10% were the 128MB version and 90% of the the upgrades have been 8 to 32MB so I'm confident that not much more than 10% of ViewFinder users are using 128MB .
AIUI JK software is almost pure magic! Well its patching of the OS had to be quite hairy
Then came along select, this complicated things significantly, it was explained to me by one of the Select programmers that it lets the VF software patch the OS and then went back and repatched the OS to suit, very messy. WIth RO6 abstracting the video driver patching patches became impractable so they had to build in support for specific cards.
JK obviously has a lot of experience of differences necessary for different cards, ROL much less so. I suspect it would be quite a lot of work for JK to change to using the official RO6 video abstraction. On the other hand I'm not sure if the relevant ROL programmers are able to divert the necessary time and finance  to add support.
 Continental users In our experience tend to go for the top of the range in our experience so I can believe that many/most of the users Steffen knows about are 128MB.
 ROL would have to try and obtain/be loaned most variants of Radeon 128MB that have been used and given the variation in output options there must be at least 3 and possible quite a few more!