I'm betting a local competent bike shop could spread the frame to fit a modern 26" mtn bike hub. I would not worry about stuff happening 2 - 3 years down the road, get your bike built up now, you seem to have a good idea of what to do, and then ride it.
I toured the top half of the GDT on a superlite w/ a bob ibex. The trailer held up, but the bob QR's bend easily, pack an extra. I'm glad I had a fully suspended bike, but that obviously adds extra issues should something break when away from town. Luckly, nothing did or has. There were road days where suspension sucked and I really wished I had a hard tail or no susspension at all. But any time I jumped back on a trail, I was happy for it. Good luck!