Having no idea about how the internal architecture of the plugin works, I still wonder what the limitations exactly are. Pentatonic, whole tone and major scales have different numbers of notes. Is there a maximum?

Also, is there a workaround for live performance purposes? Like, for example, assigning scale switches to MIDI CCs? Or do I need two instances of the plugin for two scales in a song?

Depending on your DAW (for instance if you're using Live), you could map MIDI CCs to the key and scale.