This is an easy one I think. There exists the key-command:
Channel & Track Visibility -> Agents: Show Channels that are Connected to the First Selected Channel.
A great feature, easily accessible by key-command, yet hidden a bit deep for mouse work, or touch (just saying )
Paired with undo visibility it allows for fast and intuitive viewing of group channels.
But, speaking of group channels, just beneath the R and W buttons (mixconsole), there are two (2)! empty spaces.
What I’m suggesting is: Have a button like the picture below, which acts as a toggle, and does exactly as the keycommand does. (The toggle part is that when you press it a second time it undoes the visibility change.)