What do you see as insufficient with even the best of the current mirrorless bodies and what should be improved?
Ergonomics primarily. The manufacturers want to make "sexy" instead of functional.
Also, the A7R III seems to be the only one that possibly has reasonable battery life and even that might not be as claimed.
AF needs to improve.
I'm not familiar with just how good EVF's have got, but they need to be incredible if they are to be used all day, every day to avoid eye strain. They also need to have zero lag. Are they there yet?
They've always been there if you listen to the mirrorless fanboys. Except when you come to try the mirrorless out, they have the same old problems, just perhaps to a lesser degree. I've stopped trying them out now. When they've truly pushed these inherent problems down by degree to negligible effect, is going to be many years in the future and there is going to be much less controversy about it.
Bottom line now to me is that mirrorless is for people who like WYSIWYG, video and fooling around with old lenses more than the best AF tracking, battery life and usually ergonomics. If you blast away at indoor low light action there's still no reason to pay attention to mirrorless.
