The current setup forces you to copy the entire relevant part of the rig for each toggle, which eats up the space for more complicated projects. I think having off/on toggles that layer on top of the existing expressions would hugely open up the workspace. Rather than having "coat appears on 'smile', 'frown', 'laugh'", which requires 6 toggles (smile/frown/laugh with and without coat), it can just be "coat y/n", which only requires 4 (smile/frown/laugh, and the coat). Where each new expression would require 2 toggles, this would reduce it to 1. This also means you don't need to make toggles for "smile+coat+hat", "smile+hat", "smile+coat"...I get a headache just thinking about it.
Just like, double-clicking the toggle button to set it to Isolated Mode would satisfy me. Off/On/Isolated.