I hear KDE/Plasma devs are trying to develop global shortcut registering protocol for Wayland. My proposal is to skip wayland and do more generic thing: allow to add global shortcut to jump list item. Many programs have jump list items. In my opinion, programs such like discord, could add global shortcut for unmute. This is only one example. Some KCM would read jump lists from desktop files and allow to assign keyboard shortcut for it. Additionally, desktop file could have default shortcut defined. What program must do is to call special helper, after adding new desktop file (or updating it).
KWin could inform program just like invoking normal jump list. If you decided it is not too good idea, I propose to add additionally Exec[KeyboardShortcutPressed] and Exec[KeyboardShortcutReleased] jump list entry of desktop file. If one of it exist, KWin would use these items. If not - program will be only informed about KeyboardShortcutPressed using normal Exec field.