As soon as it works. A recent update included Plasma 6.0.2 (on NixOS unstable/24.05) which apparently defaults to wayland, but it just exits to login right away. I'm not in a mood to tinker, so for now I plan to simply wait for things to Just Work. When I select "wayland" and things work and look the same (or better) is when I'm happy to rid myself of the horror that is X11, because as horrible as X11 is, it simply isn't giving me trouble these days - my system is stable and I like keeping it that way.
Edit: perhaps important to mention that I'm using a GTX 1070.
Edit 2: I realise that I'm sort of contradicting myself with how I worded the above. I don't mean to imply that I'm not willing to sacrifice anything to embrace Wayland; just that as it stands I don't think the benefits of Wayland outweighs my ability to use this computer the way I need to.