charged a kilo rate for every kg over the average -
Not a bad idea, could have worked, even, but now far too late in the USA at least where the average is bordering on obese.
So what average would an averagely obese US citizen be measured against for a flight from, say, San Francisco to Tokyo, and the return flight on the next day?
Or do we establish a global average? If so, how?
It seems to me that we're stuck with making fatties pay for 2 seats if they can't fit between the armrests on one seat, with a declaration implicit in the act of purchase that if only one seat is bought the buyer will fit in it, and forfeiture of the ticket if this is found not to be the case on boarding.
That would mean airlines must publish their seat widths for each class and aircraft, which would be a good thing for them to do.