I survived the Gnome 3 transition in Gentoo by masking it and staying on 2.4 until Mate was ready. Throughout it all I've been able to keep my wobbly windows and window decoration with compiz and emerald, too.

Mate doesn't need to be the default, but it does need to be easily installable. I never understood the "Kubuntu", "Xubuntu" etc. line of distros when the alternate DEs were easily available in stock Ubuntu. Similarly RHEL ought to make sure KDE is easily installable no matter what is their default... (Though is it common to even run a DE on Redhat?)