One can literally take ANY accordion and make it MIDI, this is just a bunch of sensors and an interface. MIDI by itself is just a digital pathway to/from the computer or modules.
What makes the Roland (and similarly the Bugari Evo) different is that they are totally digital, and yes they also have MIDI capabilities, but it is all those sampled sounds integrated inside them that they use, that is what MIDI of itself lacks. MIDI always connects to some kind of module to make it's sounds, it is these modules that most other MIDI accordions, other than the Roland, lack. It is how I can connect my Elka to a MIDI capable device like the Ketron X4, Orla 300, 800, etc... or a Roland BK-7m and have it all work together.
If Roland ever wanted to shoot themselves in the foot, they would come out with a module that has all the V-Accordion sounds and then every MIDI accordion in the world would sound exactly as they do... and I would be one of the first to purchase that... lol.
I like how a Roland V-Accordion sounds, and I like the fact that they took the time to make high quality samples of various accordions like the Dallapé, Steiriche and musette accordions (and hundreds of others), and have them reproduced electronically. That is very cool.
Ben is so right... a digital accordion is not an acoustic accordion, and visa-versa. Each is a different market segment meant for different kinds of players and each has vastly different resulting sounds and of course they work way differently. Not everyone is a candidate for a fully digital accordion, and it is expected that especially from people that grew up with an acoustic accordions, this is the segment that will be the least interested in a fully digital instrument, which in a way is a bit sad, because that is exactly the market that Roland hopes will consider their product.
Each has advantages and disadvantages and as I said, I am a bit of a strange egg in that I can live with a foot in each camp and be happy. That said, lately, I have really been enjoying the simplicity of a single acoustic accordion that was made to be an accordion, and most of my few practice sessions have been with the Hohner Morino VIN and I have been really happy with it.
That said, I won't forget my Elka, because I it does take skills that the Hohner does not require, like a coordination between the right foot for the drum breaks/solos and an intimate knowledge of your electronic equipment and how to make it all work together harmoniously.
Ben did mention something that did ring true for me. Perhaps not for everyone, but for the majority of all accordionists that I know or see or have heard, the Roland is not their sole instrument, and they own at least one or more acoustic accordions, and have no desire to become a Roland only owner.