This operation seems very specific. I doubt that Renoise has any ability to do that (diagonally place each MIDI file in a quick operation).
Maybe it would help that you share a couple of your MIDI melody files that you want to drag and drop on Renoise.
Maybe it is possible to build a “strange” LUA tool to do that specific operation.
Accumulating data or placing it diagonally is not a problem (with the iteration is possible). But we should see what Renoise does in the operation of dragging and dropping a MIDI file to import it.
It would be something like, select a folder and the tool would import all those MIDI files in the specific way you want. But I think the API has nothing related to do that. Something like:
renoise.app (): load_midi_data (filename) -- this does not exist!
Can you select all MIDI files and drag them at the same time? When you deposit them, they are stacked on the same track, each in a pattern?
Distributing data already written in the matrix is “relatively simple” through a tool. So the problem is really in the operation of dragging and dropping external MIDI files with note data.