The indicator apps are tied to the panel and would have to be completely re-written. The source code is there if you wish to contribute your time?
I remember a clock applet available for Cairo Dock, an app to track the virtual desktops, link to a volume control, network connection indicator, app menu, logout and others. You could have very little on the top panel, and some panels will auto-hide.
LMDE Mate 64-bit, LM17.3 Cinnamon 64-bit
Debian Mate 64-bit, Xubuntu xenial 64-bit, Ubuntu-Mate 14.04 64-bit, Antergos Xfce 64-bit, PCLinuxOS Mate 64-bit