Continuing the discussion from:
I think that Ubuntu MATE should follow what other OS (Windows, MacOS) and also some Linux distribution (Solus, Ubuntu GNOME3, KDE, Cinnamon) were/are doing, first is to narrow the choice of UI customization in order to focus on working on it and optimize it and give the users something more stable and looking good, because the more you focus on one spot the more you get best results.
I know "Linux is freedom", but for now that freedom can be translated to many lost/ambiguous paths by end users and will gives back the community developers more bugs that are not essentials or needed to progress the evolution of MATE.
One step of narrowing choices and which worked well was leaving only Marco as window manager which is really good decision, because it's fast and now the community can focus on improving it to get better performance and integration without being disturbed by bugs coming from other window managers.
The huge step that need to be decided in near future is to lock the layout choice to one or two choice which can be Redmond and Mate layouts, and then work on unifying, optimizing and fixing indicators on each layout.
And the last big step is to focus on one special theme/icon theme for MATE, which can be based on existing modern, good looking and popular ones.