Needs to be done
Based on Debian but separate like Ubuntu (but not Ubuntu based, though forking some of their applications and tools is always an option.)
Full emphasis on the MATE desktop and GTK3, porting programs from other Desktop Environments such as K3B and KDEConnect to GTK3. The Desktop needs to be simple to use but also allow more advanced and power users to have the control over their system and desktop that they desire.
Return GnoMenu (and rename it) to the desktop, porting from Python to GTK3 and cleaning up existing bugs. Add abilities to bring more menu layout functions and options. Should be able to work with mouse based and touch screen based systems allowing for themes to work with either or both.
Compiz and Emerald both need to be revived and Compiz needs to be forked from Canonicals current development branch. This includes returning the functions and plugins either modified or removed by Canonical to suit their Unity Desktop Environment. Integrate Compiz and Emerald into MATE to be the compositing system. Start adding Wayland support. Fix issues caused by the Unity support (possibly removing all Unity support code.)
Return full Eye Candy support and theming options. Not everyone likes the flat look being pushed on most Desktop Environments today. Users should always have the option to make their desktops look the way they want. MATE is capable of being modified in such a way when the right options are available.
Develop a ISO creation tool that allows people to create customized ISO images that is simple to use for novice and expert alike. Something like Systemback.
Things that should be done.
Finish the job of transporting Nautilus options and plugins that were available to Nautilus in Gnome 2 to Caja. While the main plugins have been done many other excellent ones have not.
Bring the options from third party tools used by MATE such as Touchpad Indicator and add them to the existing Control Center tools. (To me this is a no brainer and should have been done from the beginning. Many of these options should be native and not from third party add ons.) Consolidate the Control Center options, Emerald Theme Manager should be part of the Appearance control etcetera. Also many of the Control Center options are not properly catagorized. Case in point, Firewall Configuration (GUFW) belongs under Internet and Network not Other and Network Options under System should also be under Network, and part of the Network Settings under that. Gparted should be in Hardware not System, as examples.
Update Gkrellm and plugins specifically for MATE. Add true transparency and Wayland support. Update plugins, both built ins and add ons, to use newer tools and commands. Add support for new hardware and software. Allow horizontal placement. Add left and right click options to some of the modules (an example would be accessing the desktop calendar from the system time plugin, or accessing system power options from the battery monitor plugin.) Gkrellm itself should function as a extension of the system tray as well as a system stack monitor. Removes redundancy and declutters the desktop experience.