I owned an EML-Honda GL1100 rig and put around 50,000 miles on it, mostly highway. This was an exceptionally well sorted rig, and it was a hoot to pilot. I've ridden some very big mile days on it and many long trips. I've also traveled two wheels in Central & South America. 1) Gas economy is bad, a consideration for a RTW trip. 2) I live in a part of the US with lots of gravel roads, and the width of the track on the rig is not the same as 4 wheel vehicles. This made for handling and safety issues on gravel, an item to consider. 3) Being well sorted is important for RTW trip; ease of steering (modified steering fork or triple tree), balanced so you don't have pull on normal road camber, and as mentioned, tire wear (proper toe in and a car tire on rear). 4) I would also think shipping via container will be your only option crossing between continents. 5) I suspect in less western countries you'll be treated like a three wheel moto taxi; namely you are expected to get out of the way of the cars and trucks. Narrow mountain roads can be dangerous in this way. 6) You should know how to work on a sidecar and keep it aligned. You won't find moto mechanics with that knowledge.

Andy/TWB makes very good points.

Find sidecar groups where you live and go to several rallies. Also, make sure you own a sidecar for a year of local travel before you go RTW.

That said, I'm very much in to small cc two wheel moto for travel, with minimal gear so I can go to the difficult to get to spots where not everyone goes. Sidecar travel will be more like "The Timeless Ride" blogged by Hubert Kriegel. Both are good, have a good trip!