Question: If we are rid of the auto-gain problem, does this mean I can find a relatively inexpensive shotgun mic that attaches to the flash shoe and produce decent audio?
I think that depends on your definition of decent audio !
My feeling is it will be adequate for someone speaking to camera
Im getting my head round setting up my gear for work right now and will use the 5d on a rig for runaround and keep the 7d on sticks with a SmallHD monitor onboard and tascam sound recorder on board
sticks for interviews and hero shots - shoulder rig for picking up the rest