My attempt at emulating piano roll using the scripting API: Pianolol Melody Editor: New Tool (2.8): Pianolol Melody Editor
In contrast to the Ticky Roll it does not set new notes, but edits existing ones. It also offers logic taken from ScaleFinder to easily see if your notes are in scale.
The API does not really offer much comfort in designing these things. I couldn’t even find some way to make a scrolled sub-view or something like that. Having this natively would be more than just awesome. But I think, this tool will satisfy most of my needs fine until Renoise comes with a built in one.