content: The biggest reason for dumping X are basically that it's big and bulky and most applications just use it for basic window functions and dealing with OpenGL contexts. They almost universally do their drawing with other mechanisms and then paint it onto the window; the drawing mechanisms of the X server go unused. Once X shipped drivers, now it uses drivers in the kernel(but has to do so via the old driver interface). Anything that uses indirect OpenGL can't use a version above 1.4 and most applications are beyond broken for the client-server model of X to begin with. So, essentially, these projects are an outgrowth of the fact that most of X is legacy code and aim to replicate how modern programs actually work. If there were a serious argument about X's maintainability, they'd be wholly necessary, but so far every time the X server has run into some wall for modern programs, it's grown an extension to break through it. I'm not sure they actually any real problem.