Touring with spare 20” wheels
I would never consider bringing along a spare 26” or 700c wheel on a tour, but i'm guessing 20”ers wouldn't be too unwieldy to bungee over panniers. Yes they would be a pain to fly with because they wouldn't fit in the suitcase, and they are added weight, but think about the advantages:
1.Provided you have clearance for wide tires, you could have a main set with thinner, high pressure tires and a second pair with low pressure, wide tires if the road got rough or if you wanted to go off road for a day. It would be like making a 5 minute pit-stop.
2.If you had a flat or a broken spoke at a bad time, such as in the pouring rain, you could slap on the spare and ride until you found shelter to fix the problem.
3.If you bent or cracked a rim or damaged a hub somehow, you could keep on riding.
So, bad idea?