Exactly my point: there are better, more robust ways to do network transparency than with the X protocol.
However, it is also the case that toolkits/applications should be involved in a deep way. If I want to run an app on a phone display, it should in fact be a different UI than when I'm on the HD screen across the room.
Our current architecture is broken, in ways that are not recoverable. This is why I said I'd do it in a radically different way, if I got the chance to do it again.
Every other system out there is similarly (or worse) broken, btw, there is nothing about this rant that is X specific.