… we would expect the sender to also send to whatever was downstream… 

That’s great if you have the option to send as many program changes as you need. My looper/switcher can send two PC messages only. I have an H9 and a TimeFactor on my pedalboard but I also switch channels on my Marshall JVM410H via MIDI. Being able to receive a PC on the H9 and send one to the TimeFactor (if needed) would be great and will rid me from the necessity to buy a separate MIDI mapper device such as the Molten Voltage Osmosis.