I pointed out in that thread that sending giant bitmaps would be devastating for a major use case: scrolling windows full of lots and lots of client-side-rendered text. X has those glyphs in GlyphSets, so doesn't need to send all the giant images over again: things like VNC or SPICE do not, so a single one-line scroll of a full-screen xterm can take half a second or so under such remoting technologies, while under remote X it is nearly instantaneous (you can easily scroll the whole screen line-by-line under remote X in the time it takes VNC et al to scroll a single line).
I asked what Wayland has that provides the same speed boost over giant image lump transfer.
Answer came there none.
Apparently terminal emulators and text editors are not an important use case anymore. (A killer for me, since my Emacs, with huge windows full of lots of text, is *always* run network-remote. It's as fast remotely under X as it would be locally. Obviously it is intolerably slow over a slow remote link, but I'm not using it that way. Oh, and while Emacs supports Gtk and thus would be able to pick up any Gtk-side Wayland remoting support, I note that horrible problems in Gtk's existing support for remote X -- including coredumping whenever a display goes away -- have gone unfixed since 2002, so I am not confident that Gtk Wayland remoting would be in any better shape any time soon.)