You seem to have a more solid idea than I of what a Vison-like device is for. As far as I know, it’s for approximately nothing. I have no opinion on what I’d use a $4,000 AR goggles for besides the world’s most expensive way to watch Netflix on a plane, or the second-most-expensive monitor you can buy for your Mac (Apple’s hilarious $6K 6K monitor being the first, of course).
So I don’t think I necessarily buy that apps have to have any transparency at all. If I’m walking around doing things in the real world with a Vision Pro on my head, that itself beggars belief to me. It’s wildly impractical for that with its 2-hour battery life, super heavy weight, and hilarious appearance, and all those will continue to be true long after the 5-year window when the “26” OS aesthetic will likely persist.
So, might some future glasses or something benefit from transparency? Maybe. But if I find myself walking down the street with a screen on my face, I’d personally prefer to just close the apps that I don’t need, rather than look through them. If the glasses are going to highlight place names, people’s names, etc. they can do that with text floating in midair, like a subtitle.