I don't think there is (normally) a bypass on the mechanical fuel pump.
I think that there is an the PA28, but unfortunately I don't - have the diagram to hand, so I may be wrong in my assertion.
I can visualise a schematic loop around the mechanical pump, but then again the brain does a wonderful job of convincing you that you saw what you wanted to see
The "bubbles" in the fuel line seeling point (vapour lock?) is an interesting one, but I've never encountered that in a PA28 - IIRC the boost pumps in some Beech's are mandadted for that purpose under certain conditions (high temp.)
Your point about adding avionics to the checklist is an interesting one that I hadn't considered.
As we see more advanced kit in the GA fleet, a simple and generic "radio on, transponder to standby" clearly won't cut the mustard anymore and the aftermarket nature of much kit clearly means that the POH will not reflect what sits in front of the pilot,