If I had to select one easy improvment for the next version of renoise, this would be it :
A detachable mixer window.
For some reason, the sampler, the plugin, and the midi (??!!) windows are detachable, but what we all expect to have on a second screen is the mixer.
(add to this, hi-dpi support, multi-track recording, MPE support, and unlimited vst folders and you got an actually fully featured modern DAW)