What do you think would be the upsides?
I'll be honest, all I can think of is the downsides - cramped, lack of privacy, damp, hassle of having to move every two weeks, prevalence of rats, pain in the arse of things like post, lack of a permanent address, etc.
And did I mention how cramped it is? Tiny rooms, paper-thin walls, everything being small - small oven, small table, small shower, no washing machine.
I suppose if you had a huge boat and a permanent mooring it might be better, but those are extremely expensive. Also, boats don't appreciate in value like a house does, so it would be a big up-front cost without being an investment.
I have a number of friends who live on boats and they tell me that the waterways are getting more and more crowded. Most canals aren't exactly pretty and the safety aspect is not to be overlooked - boats are easier to break into and now that they are more likely to contain expensive electricals they are being targeted more and more.