Thank you for posting.
You raise really good questions and I am interested in discussing them with people here who know how tags work. But before doing that, let me just say, IF this is a situation where a major brand reads tags only if they are XYZ then it doesn't really matter what XYZ is or even why.
What matters is can we make Mp3tag do XYZ? That's the only thing that matters, because as a user and not a creator of Mp3tag, the only thing I care about is that the Tags are read. If they can only be read if they are XYZ, then how do I make them be XYZ?
So I am primarily interested in finding out if converting wave file tags on a mass scale to ID3v2.3 (ID3v2.3 RIFF) will resolve the problem? I don't know what ID3v2.3 (ID3v2.3 RIFF) is! It doesn't really matter but YES, whoever knows about tags here, I would be very much interested to know what that is, and why Mp3tag can't do it?
But to address your questions. JVC is a huge major manufacturer of car radios and JVC Technical Support number is 1 800 252 5722 but I would imagine that it would be next to impossible to get through to an engineer in charge of tag reading and ask why they made this change.
It would be much easier to make Mp3tag do this because this other program Audioshell, Mp3tag's competition, is already doing and Mp3tag should too.
Specifically addressing your point, this is not about the DEFAULT way.
Whatever default is is irrelevant, Mp3tag can continue using whatever it is using but maybe there should be an option (just an option) to do ID3v2.3 (ID3v2.3 RIFF) and that way, rather than making JVC switch, the big picture is what if some other major manufacturer does it in the future?
There is no getting around the necessity for this to be an option in Mp3tag.
And in the end this entire topic is about a HUGE assumption that ID3v2.3 (ID3v2.3 RIFF) is the reason why 2018 JVC models are reading tags created by Audioshell but are NOT reading tags created by Mp3tag.
I hope that the reason is ID3v2.3 (ID3v2.3 RIFF) because IF it is - then it can be addressed: Just make Mp3tag do it too in options...