In answer to all the requests, Yes, MATE 1.14 will be coming to a PPA for Ubuntu MATE 16.04. 
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However, it will be a GTK2 build to ensure nothing in your LTS gets broken. I’m not going to have access to a computer for just over a week, but the build is done. We’ll do some final testing before releasing, shouldn’t be more than 2 weeks.
can I undo this new mate once it is available? Is it a separate desktop?
How much space will it take? (I only have 12gb on a 32gb dual boot system)
Perhaps you can save me the trouble and look at this usability bug posted here.
Adding the PPA (repository) upgrades the existing desktop (1.12) to the new version (1.14). It's not separate, but if desired, you can undo this update by later removing the repository and then re-installing mate-desktop.
I don't know how much space it will take, but it could be up to 100 MB as it updates MATE's core apps too.
If you're low on space, take a look at Bleachbit (it's in the Software Boutique) which can reclaim disk space (in particular, apt's cached packages and unused localisations). 
Or ppa-purge should undo the changes for you.
Hi everyone! I recently started using Ubuntu MATE and I think it is fantastic! After trying a few other Ubuntu spins, this one I felt most at home with and I appreciate the focus on a classic desktop metaphor.
Happy to hear 1.14 will be available for 16.04 thorugh a PPA. I appreciate having the latest possible, while waiting for all GTK3-niceness of the next full release.
Thanks for you work! 
And here it is:
And here's how to install it:
