Background:
https://forum.cockos.com/showthread.php?t=237367
Basically there are vst3 plugins that don't get its presets loaded by default and provide them as vst3preset files (individual presets) on its plugin folder.
Reaper's preset importer only allows importing a preset at once, when a plugin is having hundreds of presets this is suboptimal and a waste of human time.
There are improvements that could be done to have a more advanced preset browser (and maybe share code with the FX browser), but as a starting point it would be nice to be able to select more than one preset when you click "Import preset" on Reaper's preset browser.