In the interest of fairness, it should be noted a very specific solution was tried and rejected (providing configuration variables to adjust the behavior of `register-read-with-preview`). I personally don't see anything preventing users from configuring alternate commands which call directly `set-register` and mapping those as they please, so in that sense it is still configurable. And in the extreme case you could even use advices, etc. It is very difficult to make something non-configurable in Emacs and I don't see the register system being so ingrained as to be one of those things.

Whether it's a good idea... well, I don't use registers but the whole thing seems like a bad idea to me. I don't think I know anyone who uses registers and would like the new behavior. (But I also understand the desire to modernize `register-read-with-preview` a bit. A better solution seems like it would be providing multiple implementations so users can do the register equivalent of `(fset #'yes-or-no-p #'y-or-n-p)` like every old Emacs user does today.)