I breastfed both my kids. I had to occasionally travel for business, but I just dialled that back for the first 6 months and after 6 months it was less vital for me to express both boob-wise, and kid-wise, since they were eating food too. My kids were bottle refusers anyway, so I've chucked away what little breast milk I managed to express, and those few times that I was away for a few hours in the early days, I just expressed enough in the shower to keep me comfortable.
I think the number of women who want to exclusively breastfeed and express when on frequent travel away from their < 6 month old baby must be a vanishingly small number. I'd hope that if your travel was so important, you'd be being paid quite well for it and could afford the extra luggage capacity.
I suppose on the other hand, that it's a vanishingly small number means that the airlines could make the exception too.