https://blog.netbsd.org/tnf/entry/x_org_on_netbsd_the but it's down right now.
https://news.ycombinator.com/item?id=40269680 is about that article, but it's a long discussion with a lot of it noise. If this information is there, it's difficult to find in it.
If NetBSD's improvements were going to be upstreamed, it would have been done. And why put permissive code in a place where more easily a GNU distribution will use, take credit for and not give back improvements? If they want it, let them find it on a BSD repository. People don't understand that they often don't want improvements there, as they like their project how it is with Linux bloat in it. They don't want it improved. It's why NetBSD's fork is about to make unrestricted improvements, bc it gives them room to do so without pushback. NetBSD's fork is so different than X, that it simply can't be dropped in anymore for FreeBSD. It would have to be ported separately.
They don't want NetBSD's X implementation discussed on Bugzilla. They want it discussed on the X mailing lists, however, they would have done it already, if they were going to do it. Secondly, NetBSD's is too different. And as I already wrote, that needs to be downloaded from a BSD site, not from a freedesktop site. It could be brought up on FreeBSD's mailing list, but Broadcom VideoCore drivers, some about NetBSD already having them, have been brought up a few times on there by different people, and no one hardly responds to them. They would probably shut that down, and say to use X's mailing list. I already stated why it's better off as a BSD project than an Xorg or freedesktop one.
Since the site is down, so I may have written the name wrong. No one has it except NetBSD. Linux might have it, but if so, it's not as good as NetBSD's.