nickmcummins mate-desktop-1.15-gtk3 was added to the AUR (arch linux user repository) today. Of course, it’s still very experimental, but advanced users may be interested in giving it a test drive. I must say that I am pleased with what I have seen thus far, most notably that the MATE appearance/theme util now finally displays theme previews correctly!
See MATE desktop releases for official downloads.
A word of caution: I have observed some high CPU usages on the Xorg process with this beta version of the MATE desktop. The Xorg process hovers around 8-10% CPU constantly. I ended up uninstalling and using Xfce4 which is much less CPU-intensive.