Indeed there is. Roon has the technical capability to display the png transparency, like this experiment shows (no matter if the source is square ore not):
Album detail:
Now playing bar:
Recents:
But for one thing Roon does create small thumbs as jpg no matter what the source format - so transparency gets lost. And for a couple (not all) picture areas a background colour is defined which defeats the transparency effect as well - like in the now playing screen, where the square image placeholder seems to have a black background.
As for the feature request, I suddenly remember something:
I wasn’t aware of the placeholder backgrounds, not sure if Now Playing screen existed back then…