There are plenty of bike travel cases for 700c bikes that work with airlines. For example, Ritchey itself sells a travel case that works with their 700c Breakaway bike.

Otherwise I would still look at 26". There are relatively lightweight rim options out there. Here are some that are under 500g a rim. Some of these are discontinued but I know for a fact you can get the Aeroheat. Plus there's a host of vintage MTB rims that are pretty light.
-Velocity Aeroheat
-Mavic XM719
-Sun Equalizer
-Stan's 335

You couldn't pay me to ride 26"x28mm Gatorskins. Compass/Rene Herse has a variety of 26" tires under 2" (including the 1.25"/32mm Elk Pass) that are going to weigh a lot less and feel way better on the road, not to mention being faster than the Gatorskin. There's also a very lightweight tire under the Fairweather brand made by Panaracer that uses the Pasela tread mold but with a very lightweight, supple sidewall, that will ride better and faster than a skinny tire like the Gatorskin.

650c would be the method of last resort for me. It's just not a good wheel format if you are looking to own the bike for a long time.