No, not a Reaper guy. Just thinking logically.
To be honest, there is not much that I would change in Minimalistic (front) GUI. I think overall layout design is OK. Few exceptions are the "Radio" bar (top thing) that you can't remove, but it was said to be considered to make the view optional, and pretty useless navigator when you get to about 100 bars. But that is another conversation smile
Other than that, floating elements such as transport, tabbed toolbars and true customization > making user buttons based on existing shortcuts would be a very nice GUI feature. Or improving existing GUI, whatever you want to call it.