Sometimes, when opening an old project, the first task is to try to remember what you actually did, mix-wise.
 
What would be handy would be an equivalent of the synth rack, but for effect plug-ins. This would show all the plugins used in the current project, ideally with an annotation saying what track or bus they were on.
 
A good additional feature would be per-plug meters showing how much CPU power each was using. This would be very handy for tracking down causes of drop-outs.

Along similar lines, perhaps a track list + the plugins used per track, in say a text or XML export from the project?
 

The meter could also be a Control Bar Module with tiny indicators for each plugin that are ON/OFF clickable so you can find issues by process of illumination elimination. That way it only takes up screen space when you want to see it.

Hmm, interesting. I think what I'm after is some virtual equivalent of being able to see racks of outboard and a patchbay. It's just another way of looking at data that's already there, without having to go hunting for it.
 
So yeah, your control bar module idea is kind of like the patch-bay bit.
 
Of course, this could all get hideously over-complicated quite easily. The main purpose (for me anyway) would simply be able to see what's active in the project.