Fully agree with the sentiments, I say make it total weight (weight + baggage) per pax (adult). I think some of the Yank carriers have the right idea, charge the large pax for 2 seats but refund them the extra seat if the flight isn't full.
Baggage allowances aren't the worst of it though, having to sit next to one of these weight challenged pax is very unpleasant on one of the 4 to 5 hour transcontinental flights, spilling into your already somewhat limited seating area.
