There has been an interesting news from MATE developers. They are planning to release MATE 1.12 by the end of this month or in November based on testing. They adjust the development cycle to follow Fedora/Ubuntu release schedule, approximately around 6 month, but there is a feature freeze period for each Linux distribution, so it's very small time frame for adding new features into MATE.
I was planning to build MATE 1.12 for next Slackware and provide GTK+3 build, but that seems impossible as Slackware 14.1 still stayed at GTK+3-3.8, which is very old. I'm looking for possibility to build MATE 1.12 for Slackware 14.1 since they have bumped several dependencies to a newer version and i'm afraid there might be some dependencies that can't be met by Slackware 14.1.
At the moment, i'm building MATE 1.11 on a clean VM and if it turns out to be a success progress, i can provide MATE 1.12 for Slackware 14.1. Current users have no worries since they will be able to compile from sources without having any problems.