However, I've been contemplating the idea of creating a smarter auto-placement for new boards where it'd take the relative positions on the schematic into account. As in taking the relative distances of parts on the schematic, probably using a weighted heuristic / k-means to determine part clusters.

That'd be about 80% of what I'd want from a full auto-router. The new S-Expression eschema format should make it almost trivial to do as an external program. I tried on the old format and it was way to difficult to parse. Though if the Python API's really have been updated then it could be made into a plugin.