I’ve been keeping an eye on this thread and it does seem unfortunate that not one word has been provided by a member of the Ubuntu MATE development team.
It is really disappointing.
I have decided to move on to openSUSE Tumbleweed but I enjoy keeping tabs with this wonderful group (and out of interest, how things are developing with this). For me, I have realised the traditional desktop is the most important thing rather than GTK3, and I have found a good home in the LXQt desktop.
To be honest, though, I don’t stray far from the MATE (GNOME 2) workflow. This is my desktop (if anyone wants some inspiration):
