My main issue with Wayland is the fragmentation. Abstract protocol which could be implemented by particular DE/WM means nothing to a user which now doesn't have a guarantee that their tools will work under all environments. For example, some screengrab utility could work under Gnome, but will not work under wl-roots based WM just because the relevant protocol is not supported there. That's a major drawback to me, we lose flexibility and kinda forced to use mainstream DEs where they have enough devcapacity to support most of the features from Wayland protocols. Contrary to X.Org where most of the functionality is implemented by server itself and protocol exposed to the clients is way simpler.