Here is the idea:
You run interactive rendering in floating window, minimise it, and when it's minimised, it would automatically pause itself (to save system resources, make everything run smooth). After you do some changes, just bring IR back with one click and it would start refreshing again.
How is this different from hitting F9? It gives faster preview, and you can do some real-time tweaking with it (set desired camera angle, tweak materials - the stuff you usually do with IR).
How is this different from IR docked in viewport? You don't have to sacrifice one viewport for it, it doesn't eat additional system resources so you can work with heavy scenes.
btw, now when IR is minimised, it is still rendering, and pops up every time you change something in scene - I don't like this behaviour
So now the final question - is this even possible? :)