Since the introduction of PulseAudio to -current branch along with all the supporting packages including the deps (mainly gtkmmX packages), some of the deps that were previously available in SBo and also MSB project are now gone since it's now included in -current.
For me personally it's a good news. I can get rid of around 5 packages in my MSB packages, which leads to less build time and have faster release when Slackware 14.2 gets cleared for public. My list of packages to maintain will be lot less now. When someday we are ready to move to GTK+3 build, the list of additional packages needed are getting smaller as well since gtkmm3 is also included in current.
Overall, it's working very good now. The upstream developers have fixed some of their roadmap entries which will lead to MATE 1.14 someday this year.
At the moment, i'm building MATE on a new fresh VM to test out the list of packages and build orders.