Does no one else ever use X applications over an SSH tunnel? It's an easy way to, for example, control the music playing on my Linux box hooked up to my stereo system.
In all the blog posts about replacing X, I don't see anyone even mentioning this feature of X. Or if they do, they say that its an irrelevant feature.
In all the threads I've read about Wayland, there's been considerable hyperventilation about loss of network transparency along with assurances that those concerns would be easier to deal with in a post-X world; basically, that the people working in these problems weren't born yesterday.
(1) They refer to vaporware features that the upstream developers have explicitly rejected: seriously, read the upstream mailing list.
(2) They refer to a two-tier world where some old X apps will still work remotely, while all new apps won't work.
(3) They refer to VNC and RDP as acceptable alternatives, even though these are inferior because they forward the whole desktop, require you to install and run an entire desktop on your remote server, refer to vaporware rootless RDP which doesn't exist on Linux, and don't deal with trivial items like pixel-size incompatibility between server and client.
RDP has included the ability to forward individual windows. RDP also includes a lot of capabilities that (as far as I can tell) X11 doesn't like bidirectional audio redirection, redirection of local hard drivers, printers, etc.
Frankly, the user experience for remote desktop and remote application access with more recent versions of RDP (in Win2008, etc) is vastly superior to what's currently available for remote desktop and/or application access in Linux.
Now admittedly, I don't know of an RDP server for Wayland that implements those features (or any RDP server for Wayland really). But given that Wayland is still fairly young that's not surprising. There's certainly no compelling reason why a good RDP server can't be written for Wayland.
Have you taken a look at mpd and its accompanying CLI frontends? Tunneling X applications over SSH isn't popular because there's almost always a CLI application that accomplishes the same thing.
I have only ever used X over ssh, at least as far as running applications remotely. Particularly when I'm on a windows box - putty + Xming is fantastic.
In all the blog posts about replacing X, I don't see anyone even mentioning this feature of X. Or if they do, they say that its an irrelevant feature.