*** Hit post reply, but nothing happened - I guess I should've had a notification page about admin approval? - so if it's double post, please excuse me ***
That's right, though it does not make things easier - I mean, I have ~300 windows VSTs (I don't have LADSPA or other type of plugins in Carla), so it's kind of hard to keep track of them. What does this "K1Ks" plugin do? Is it an analogue synth, a sampler? Can't remember... and can't google for help every time.

In the meantime I tried an other VST bridge, LinVST, which seemed OK because - theoretically - the bridged VSTs would show up in Reaper's FX list so I could put them in folders. But I ran into some compatibility issues (I think), one or more of the VSTs doesn't like LinVST: after re-scanning the FX folders (no issues here), Reaper just wouldn't start (it froze in "Initializing" stage). Not having any error messages or logs to trace down the culprit, I had to give it up and drop LinVST.
I just installed Airwave, looks interesting, but as far as I understand, it only works one-by-one, manually, there's no batch processing? Well, it's worth a try, maybe I can just pick a few cool VSTs, who needs that many, right?
(...a few minutes later...)
So, no joy with Airwave. The bridged plugins cause Reaper to freeze first at plugin scan, then at restarting Reaper.
That's too bad.
Andrew