The publishing of v1.0 of a protocol has little to do with the stability of software implementing that protocol. The software in question is in fact KWin, the KDE window manager. It is the most mature and featureful Wayland compositor, and the KDE devs have done a lot of work over the past few years to get it competitive with its X11 backend. However even they themselves still consider this a transitional phase: https://www.phoronix.com/news/KDE-Wayland-Is-The-Future

Also, time is in any case less relevant that developer hours. Were I feeling snarkier, I might point out that GNU/Hurd was first released in 1990 - perhaps we can finally switch to that...