I have only recently added a MIDI keyboard properly to my renoise set-up and a thing that I would find particularly useful would be a command/ keyboard short-cut to delete all note-offs in a selected range. i.e. leave all other pattern data unaffected.
A Ctrl + x but for note-offs only.
Also a new add note-offs command would be sometimes useful.
Ctrl + Caps Lock is a really useful feature but a further command would be great too where a note-off is added to every empty column in a line, in a track. Maybe shift + Caps Lock. All notes already present in that line would be left in tact with this command filling in the gaps with note-offs.