Thanks for a fascinating analysis! ^
I think that when one looks to certain international routes, perhaps not TATL or TPAC, the /UPDI mechanism goes into the lower fare buckets more deeply.
I've got a YVR-EWR trip next week with a fare code of:
LNN1A9SS/UPDI
It's priced around $800 USD round-trip, and includes a return on ps EWR-SFO-YVR.