Well, I've been on this search for a month including a spreadsheet. The 2 I am most interested in are Osprey Ozone 42 liter wheeled carry on (4.5 pounds) and TravelPro Maxlite International Expandable (5.4 pounds) which is a 20" case but length including wheels and handle is 55cm which is what many International luggage guidelines are. Unfortunately both of these are sold out on their respective travel sites but the Travel Pro International is available on Amazon but not sure if quick shipping is available.
I have the Rick Steves 20" 2-wheeler but it is 6 pounds which is more than I want to carry. I may be forced to use it if the Ozone does not come back in to stock before my September trip. Mine is very old and I believe is a bit smaller than the one he sells now. It also has the molded plastic back on it so it is not as squishable as I want but your needs may be different.
Where are you headed? I saw a bag that I am literally drooling over from the VanGogh Museum in Amsterdam BUT it costs 75E to SHIP so no, not going for that!