People asked for it, we delivered! The next release of MATE Tweak will support more window managers. Marco, Metacity, Mutter and Compiz. Ubuntu MATE will not ship with Metacity or Mutter pre-installed but if you install them, MATE Tweak will adapt 
Proof it happened.
Will this version come to 15.04 or not until 15.10? (I don’t mind, just curious!)
Ubuntu MATE 15.10, back ported to 15.04 and maybe back ported to 14.04.
This is very awesome, especially the Mutter support that is interesting.
For Ubuntu MATE 15.04 users who fancy testing you can add the following PPA and simply:
apt-get update
apt-get upgrade
This will get the new MATE Tweak and the updated ubuntu-mate-default-settings.
The settings package includes some fixes and better organises the System menus after you logout and in again. If you want to test Metacity and Mutter you’ll also need to install them.
apt-get install metacity mutter
Lastly you can also install some additional menu entry tweaks.
apt-get install ubuntu-mate-libreoffice-draw-icons ubuntu-mate-libreoffice-math-icons
Enjoy 
Great! I’m waiting this for 14.04.
awesome working wimpy!
How about changing the wm button order in mate-tweak . I mean custom like you edit them in dconf-editor or xfce wm settings or like cinnamon wm settings
The order currently makes sense, starting with simple and lite and progressing to big and fancy.