It's in Wayland in the same way everything else is, i.e. fractional scaling is now a protocol included in the standard protocol suite.
> Because what is probably 90% of wayland install base only supports communicating integer scales to clients.
As someone shipping a couple of million cars per year running Wayland, the install base is a lot bigger than you think it is :)
Hmmm, sorry, but I don't care about install base of wayland in a highly controlled environment (how many different monitor panels you ship is probably less amount of displays with different DPI in my living room right now).