By accident I had gui-libs/wlroots-0.12 installed and tried to compile gui-wm/wayfire-0.5.0, which failed. So gui-wm/wayfire should not depend >= on gui-libs/wlroots, but stick to "major" version.
This is unfortunately not going to be possible.
The ecosystem is heavily evolving and at a very fast pace.
If we try to do version restrictions everywhere, its going to be unmanageable very fast. Also the fact that different window managers all need differing versions of wlroots makes it very hard for us to keep everything sane.
In general, when dealing with wayland, I'd suggest asking the upstream authors about compatible versions.