I was intrigued to see a button-accordion style keyboard being used by accordionist Karene Neuville in this video:
https://www.youtube.com/watch?v=oxmkTsE1UXkI'm not sure this has any advantages over a MIDIfied accordion? I presume it's a custom instrument, as I can't find it on Ketron's site. If it can send MIDI messages it should be able to control Hauptwerk, and it might facilitate the playing of some types of pattern which are awkward on an organ keyboard? More for theatre organists than classicists, but an interesting development