It would be cool to be able to have the master Spectrum Meter and Phase/Stereo meters show by default in the large Mixing window. It would minimize with your Mixer window. And we can have an option to display the Spectrum/Phase meter within the Mixer window and turn it on and off.
Right now, you have to manually add those plugins and then either use the tiny minimized display in the plugin part of the fader, which is very hard to read, or keep the plugin open and pinned which can take up a lot of screen real estate, covering your tracks and faders or arrangement, and forcing you to minimize/re-open it if it's in the way. You don't usually need to see the Spectrum meter when in Edit/Browse mode but it would always be helpful in Mixing mode.
Think of the fancy pro guys who have the spectrum meter on their desk, if we can dock it so it's always visible in the mixer, we can work like that. In my head, I see the tracks and busses in their regular spot, just with a smaller scrollbar; the (optional) Spectrum/Phase meter would be next and take up a good enough chunk to be easily visible; and then to the right of that would be the master fader.
Maybe the optimal thing would be able to dock plugins within a window, like Visual Studio lets you move stuff around anywhere. and then lock it in that position. But I could see that being a much bigger lift. But it would also be cool for things like compression plugins, let's say I wanted to dock my mastering compressors plugin screen into my mixer window, I could do that too.
The difference between my proposed wishlist thing and the existing "floating plugins" being that this wishlist item means there is no "overlap" of the plugin being on top of and hiding something else, but that it fits into a window and thus doesn't cover anything up, and also minimizes and maximizes along with its parent window.