"This is free software", only now all the other distros have to look at everything for which RH is the upstream and which is critical for boot and figure out how many of those things now require / and /usr to be on the same filesystem or require hacking to fix it -- hacks which upstream will surely reject, so they need to be forward-ported for eternity. It's not like the symlinks for compatibility will work if / and /usr are on different filesystems and /usr is not mounted in early boot when a lot of this stuff is needed. You know, like almost every Unix system for the last thirty years.
Unless what you're proposing here is that everyone else follow on and eliminate /usr as a separate filesystem -- which ignores the installed base of systems -- your suggestion is vacuous.
But, hey, why pay attention to little things like the installed base or little things like other distributions perhaps not wanting to scrutinize every single commit in the software they get from other distros in case bombshells like this are thrown in. We use Fedora, we don't care what effect our decisions have on other distributions. (Several upstream maintainers of critical software who happen to work for major distributors have this attitude -- in each case picking a different distribution as the one you 'should' use if you want to use their software -- and it is utterly odious.)