I would second this, it should be better integrated into the EPM. The EPM already does this to a degree, but you have to click a button on each mapped extension to see its status. There’s no general overview like this, other than on the Asterisk Info Report page.
The one thing I do to see currently registered lines, while also getting some details of the registration, is by using:
asterisk -rx "database show registrar"
I’ll combine that with a variety of cut commands to clean it up more.
But having a clean, simple overview like @sawgood1000 mentioned would be nice.
FOP2 and EMP together do everything in the OP’s wishlist and more - just not “green light, red light” Registered extensions in FOP2 are green, unregistered extensions are grey. FPO2 is not terribly expensive for all of the features it includes ($50 as I recall).