So far, i have been building MATE and Cinnamon under 14.2 stable releases and i will continue to support 14.2 as long as possible. It's a rock solid release and all MATE and Cinnamon updates are coming in smoothly.
Current is now progressing as well, even though no major changes in the toolchain and libraries, making it possible for packages built against stable be used under current machines. That, however, is not a long term solution as current is a moving target, meaning it will diverge from stable when Pat pushed the big updates someday with all the changes from toolchain, libraries, and applications. Mixing current and stable are not recommended.
Today i created two new VMs for building MATE 1.17 and latest Cinnamon 3.2 packages against current for testing area. Both have been uploaded to slackware.uk repository (MATE, Cinnamon) and it's available in x86_64 architecture only. These packages can be used to generate new Slackware Live ISOs using liveslack script from Eric Hameleers (AlienBOB).
Please note that these packages *may* break when some packages in Slackware is upgraded someday. Sometimes a simple rebuilt will fix it, but there's a chance that it may need more patches to fix the issue. That's the fun part :)
Enjoy MATE and Cinnamon packages for Slackware-Current users.