XLibre is a joke. They're making changes for the sake of changes: for example, commit aefde9 strips out vendoring in an ad-hoc, incomplete fashion (introducing a minor spacing bug in the process); and commit aafd986 replaces `int` with `unsigned int` (instead of `size_t`), failing to properly fix the bug that the compiler warnings identified (albeit, also removing an unrelated C footgun along the way, so this does look like a bug fix). The main author has a history of cowboy commits: 533c45e (which made it into mainline Xorg before he got kicked out) straight-up prevents ‎hw/xfree86/os-support/bsd/arm_video.c from compiling, so it's clear there's no actual testing taking place.

I doubt the XLibre authors understand the X security model, either – they never do, in forks like this – and they've alienated most of the security researchers who might otherwise clean up after them.

Phoenix and Wayback are much more interesting projects, in my book. Wayback's designed to actually work, and I expect it to be production-ready much sooner; but I expect Phoenix to be the more technically interesting project, since it's deliberately breaking from the X11 spec.