I think you are mistaken, MATE does have very vibrant and development and
does have active updates, yes all the programs will stay the same feature
wise, but why fix what isn't broke?
And Linux Mint does ship with MATE as default, in fact they RECOMMEND it and
do active development on it.
http://linuxmint.com/rel_maya_whatsnew.php - MATE is even listed before the
Cinnamon desktop on their release page.
"Both the MATE and the Cinnamon edition were built with the highest quality
of integration and will be supported until April 2017."
