We have arranged a new git branch called current-mate-1.6 in our GIT repo that will serve as the base for building binary packages for Slackware-Current until Slackware 14.1 gets finalized. When it's released, we will rename the git branch into 14.1-mate-1.6 and this will be the new stable branch that are officially supported by us.
What will happen with the "1.6" git branch? We will rename it into 14.0-mate-1.6 (to be consistent) and we will leave it as it is. You are free to checkout this branch and use it to update your MATE packages if you are still running Slackware 14.0, but no binary packages will be provided once Slackware 14.1 gets released. You can still build your MATE packages from this branch.
When MATE 1.8 gets released (probably next year), we will move on to support MATE 1.8 on Slackware 14.1 (or 14.2 or 15.0 when it's released) and a new branch will be made for that purpose.
Speaking about MATE 1.6 for Slackware-Current (14.1), i have tested here with virtual machines on both arch (32/64 bit) and they are working fine as expected. They are the latest Slackware-Current updates per 25 September 2013. The number of packages included in MSB has been reduced since there was some packages that are now included in the default Slackware installation.
For those running -Current, you can also try this version by checking out the current-mate-1.6 branch and start building MATE packages.
Here are some screenshots of MATE 1.6 running on 32 bit (above) and 64 bit (below).