A trick and a small bug
Hi Rui, I'm back again after a while. :)
I wanted to mention a couple of things:
1. I've solved the problem of dragging and dropping files from Samplv1.lv2 and Drumkv1.lv2 by editing the .ttl file corresponding to the UI and leaving only the lv2#ui_external version.
It seems to work well in Qtractor, Ardour, and Muse. I'm sharing this trick in case it's useful to someone else. (Enabling the option to select different UIs in Qtractor was cumbersome.)