At what level do you actually play these games? Honestly curious.
I can personally state I'm completely disinterested in relearning Project DIVA with altered symbols, just like I would stop playing DDR if they changed the order of the columns. It takes a lot of practice and learned pattern recognition to play any rhythm game at high levels, and an alteration to the symbols throws all that out the window.
I am not advocating they don't try to bring back some form of Vocaloid game, but it doesn't have to be Project DIVA. (And, as I keep saying, Project mirai 2/DX's system is already Switch-ready.)
Fwiw, I play exclusively on Extreme and consider myself pretty decent (although I doubt I'm at your level). I think the symbols are a big, legitimate problem, but
if the developers found replacements that worked, I'd be perfectly willing to re-train myself.
I'm just not sure what those symbols would be. Arbitrary shapes without a clear relation to hardware buttons would be
much more difficult to learn, and I really don't think letters or diamond icons would be distinct enough. Arrows might work, if they could find an alternate way to handle double notes, but I'm still not sure they would be as easily identifiable in a fast stream. Arrows work for double notes because double notes are less common.
But, I'd love to be proven wrong. I enjoy Project Mirai well enough on the 3DS, but I don't think the gameplay is nearly as good. Project Diva's flying notes are my favorite way to represent music in an a video game, and the primary draw of the series for me. They're exciting and flashy, and their movements match the music and PV's in creative ways. The note patterns feel intuitive and instinctual, but they're also
just difficult enough to read that you're forced to
rely on those instincts. Mirai has some of these qualities, but not enough.