The problem with that strategy when it comes to desktop software is there's no way for the developer to know what the user has done (unless the software phones home, which is a no-no when it comes to privacy-respecting open source software).

If it's a SaaS API or a web application, the developers can look at access logs or analytics to determine what endpoints and features are being used, and when users need to go back to the deprecated interfaces to get what they want.

There's no way for a KDE developer to learn "$NUMBER users went back to X11 because $FEATURE is missing in the Wayland version".

(Of course they can ask their users, or hope that users file issues on the bug tracker, but things will definitely fall through the cracks via these imperfect communication channels.)