Well, first let's define "MIDI". We all know it means Musical Instrument Digital INTERFACE. The interface part is the part that is important. You can have a instruments with internal sound capability with MIDI and not use the MIDI, but you cannot have an instrument with no internal sounds to be of any useful value without using MIDI and connecting it to an external module.
MIDI is a wonderful technology thats expanded to include not just the ability to activate sound on remote modules, but to interconnect and control. If it wasn't for MIDI in my setup, I'd not be able to have a wireless foot switch reprogram my 8X via the MIDI input or send controls to activate a start/stop sequence to the BK-7m via MIDI and a ton more.
MIDI is a means to an end that opens a world of possibilities compared to what it was 40 years ago... and the Roland V-accordions are *not* MIDI accordions, they are digital accordions *with* MIDI integration.
