Well, there are two components to my question, really. Firstly there's the puzzle of working out what would be possible. Secondly, there's actually piecing together a route that I'll take. I'm based in Europe and have already travelled around most of it, so I'd like to maximise the non-Europe parts on a RTW. For the sake of this question, I also expected it would be too simple to come up with a route where every coupon gave a different country by hopping around Europe a lot. Removing Europe from the equation gives some more interesting routes.