How about instrument specified color background behind start and stop in pattern to visualize note lenght?
…just mentioned that in another post, but since it is most likely a very easy thing to do, i figured i should add it in here 
Yes, been opted/mentioned many times before, tho can transform renoise in a mismash rainbow of colors imo.
In good old protracker you had vu meters that helped visually to decide if a sound was still playing. The scopes are sufficient most of the times, but when you have a very long sample spanning over multiple patterns…a visual clue where the sound ends could be very helpful when programming.