People keep saying this was "decided" for security, but usually with no sources cited. I wasn't able to find a firm decision and discussion/roadmap. Instead it seems more like it was viewed as "handling this in a secure way is hard, let's skip trying to figure it out". Which is pretty sad, since as far as I can tell users didn't really get much in the way of tangible benefits from Wayland aside from security (altho the KWin maintainer points to Wayland being easier to test automatically https://blog.martin-graesslin.com/blog/2018/01/kwinx11-is-fe...).
I found a RFC on a mailing list: [RFC] Interface for injection of input events (https://lists.freedesktop.org/archives/wayland-devel/2017-Ma...) where the xdotools maintainer chimed in with some thoughts. But it seems to have died quick.
I then scoured the Wayland freedesktop bugs (https://bugs.freedesktop.org/describecomponents.cgi?product=...) and one of the closest things I could find to a discussion of related issues was an open bug "Add an API for taking screenshots and recording screencasts" (https://bugs.freedesktop.org/show_bug.cgi?id=98894) which has to deal with similar security challenges.
Ultimately I, along with other automation-minded folks, will be sticking with x11 until this is figured out. macOS also has a decent automation story, with tools like Hammerspoon, Automator, and so on.
I've got a fair bit of other notes on the topic which I can share with anyone interested - for example I saw "Some way to inject automated libinput events?" (https://bugs.freedesktop.org/show_bug.cgi?id=99800) where the person was actually trying to tune a gamepad.
Also see https://www.reddit.com/r/linux/comments/7bm9az/what_cant_be_... where people are saying that Wayland is further fracturing the Linux desktop world.