Network transparency - sure, they say "we'll just layer it on top, it will be easy and work well". But so far it is a no-show. I also haven't seen whether or not it would be possible to do single windows like X, as opposed to full desktop.
I've written about it before, sick of repeating the full spiel about why whining about Wayland's remoting is silly. It's possible. Nobody's done it because nobody who actually matters has cared enough to implement it. If you care about it, implement it.
Then there is the client-side window decoration thing, which is just stupid.
And the "you have to write a compositor to write a WM" thing seem iffy to me.
I am not sure how big a problem this is, but it was not reassuring the way they first talked as if there was no possibility of WMs. Just a misunderstanding, it seems, but the compositor may still be an issue.
Nothing wrong with that, either. The world does not need 400 different broken WMs when just one good WM does all you need.