Rear flat on an IGH with a drum brake sounds like an awful roadside repair job anytime of the year. But I think the idea is really clever. Correct installation could be a real challenge considering how many people seem struggle with setting up just one tube properly, but I think it could work really well.
On the other hand, if you are considering buying a set up like this (IGH, drum brake, chain guard) you should do it with the full knowledge that rear flats are going to be a huge pain to fix, and you WILL get a flat rear eventually. I'm thinking that particular feature is not talked about much on the sales floor.