My tourer is pretty much what you describe, an S&S coupled 26" mountain bike with a Rohloff. It is an excellent, functional travel bike.



My international kit packs into three pieces: an S&S 26x26x10 hard-shell case, and two Arkel panniers:



The Old-Man Mountain rear rack fits into the box with the bike, along with water bottles and miscellany, and it comes in within regulation size & weight. I check the box and one of the panniers, and take the other as carry-on. The really nice thing about the kit is that I can handle everything at one time solo, which would be pretty much impossible with a bike box. The S&S box fits into taxis and train luggage racks like any other suitcase. Don't let anybody tell you that there is no advantage to be had with a coupled bike. The advantages are many. Basically, the coupled bike becomes equivalent to any other suitcase, instead of being a "bicycle", which for some bizarre reason freaks all sorts of people out when getting on trains or airplanes, checking into hotels, taking taxis, you name it.

The easiest thing to do with the box is to just leave it at a hotel near the airport and pick it up again on your way out, but as you mention, that requires a loop route of some kind. The other option, which I will be using in Spain this summer, is to ship it from a UPS office at your departure point to another UPS office at your destination. You can pay for the shipping and print out labels before you leave for your trip, then just tape them to the outside of the box and drop it off before you leave. UPS shipping offices are pretty ubiquitous in Europe.

The only other thing I might add from experience is: expect to have the suitcase searched by TSA. I tape packing instructions, with photos, to the inside of the case so that the TSA goon has a least a fighting chance to get it back in the case properly.