Take a look at this article by Lennard Zinn. He filed away the base of a standard 10-speed freehub body on a Shimano 29er wheelset to use the wheels on his 11-speed 'cross bike. I'm not sure whether this would work with a standard Shimano MTB hub, but the XT hub I looked at had a similar lip at the base of the body that could be filed away, but the spoke positioning is a little different than on their pre-built wheels, so may interfere with the rear derailleur.

Another option is if you want to wait until Shimano release an 11-speed compatible disc hub (this might be a while, but with the way things are going, they must do it eventually), then you can fit 10 of the 11 cogs from an 11-speed cassette onto an 10-speed hub and then still use the 11-speed shifter and derailleur, and just block the 11th position using the deraillleur limit screws. This could be an interim solution until you figure out what to do for the final wheelset.

I'd also been thinking about going 11-speed on a lightweight touring rig that I recently built up. Having the increased cable pull per shift that the Shimano 11-speed shifter uses should make the shifting more reliable than with a Shimano 10-speed setup; but as well as hub availability (this bike also uses disc brakes), the other downside would be possible problems sourcing an 11-speed chain while on the road if there was ever a problem - I'd imagine that 10-speed stuff is a lot easier to find a source for when outside of major urban areas. For you during PBP, this shouldn't be an issue since the support vehicles should have something if you need it. I therefore opted to stick with 10-speed stuff and so shifting is fine, although not flawless.