Got my script working and completed (with parallel processing, ooOOooOoo) and have the individual labels as .rpy files. Attached in case you want to take a peek. Previous upload was only half-complete because of a dumb logic error in my script (skipped every other label because stupid). Edit: removed some test labels I was using that aren't stock.Heh. Check out the code for the blackjack game from Book 2 if you haven't already, that's always fun.
If you're serious about working on this thing btw, it might be worth looking into the actual Ren'Py parser before doing anything. As far as I remember it does store things like lines, labels, jumps and variables in some kind of data structure, so there might already be a list containing every label as a list of dictionaries or something similar.
Included the label separator powershell script for reuse/posterity.
Haven't looked enough into the renpy parser to see if it can be used for mapping specifically.