Building the tip of mesa and xorg is a major undertaking which is likely to break every
package on any given system. Nevermind the minor fact that frequently the tip is in an
unbuildable or incompatible state.
For my own code, I follow the policy of taking a bug report seriously unless I have reason to
believe that it has been fixed in a newer revision.
I believe there was a long and thoughtful post on linux-kernel regarding this very issue
recently, where the author (a major kernel developer) concluded that it's counterproductive to
insist on testing with latest-test-rc-mm.