Collapse Groups in User Toolbars

Would it be possible to collapse and expand groups in the User Toolbars by a double click at the group bar? This would reduce the need for scrolling.

Unfortunately I didn't have the time to play with Nvil in a while and probably won't be able to in the near future. But I was curious about the User Toolbars. As I said, I don't have time to set them up, so can someone make screenshots of what you can do with them and how they look and work in the GUI?
I'd like it best, if they could be arranged like the shelf menu in maya, that means having registers for the toolbars. I know Nvil can have registers that bring up the window if you hover over it. So can I make different user-toolbar-registers by pinning them to the top? Would they always disappear again? Or can I switch between toolbars and there's a permanent display of the content of one chosen toolbar?

User Toolbars are like any other toolbars. You can dock them the same way, you can arrange them the same way. But you can manipulate the content and add buttons. With and without images. Hard to explain, it`s really easier to load Nvil and have a look by yourself

done.