Definitely want to follow this, what your friends wind up doing. Seems like something to try, rather than to commit to long term. Renting a secure, dry, storage facility for all one-of-a-kind possessions would be a must. Buying a really nice "houseboat" that's already berthed somewhere on some (often artificial) inland lake somewhere sounds like a colossal bore that costs too much. If it's to be an oceangoing vessel of some sort, probably need something to protect against pirates.
There are a lot of inland waterways here in the states, or for that matter, you could do the same in some other country. When you get tired of a place, sell the boat and buy another somewhere else. A person might even make a little off the sale, if they got the boat at a good price and did a little work on it. I see no reason why someone couldn't flip boats like houses.
I suppose there isn't any reason you couldn't do the above in a boat capable of crossing an ocean too, in-case you ever needed to.
Inland cruising is something I've considered myself, since I can't handle the ocean - I get sick every time - but there are still places I've not visited in the RV.
I'm anchored to high-speed internet, a workshop, a bunch of hardly used toys, my dog, small garden, Walmart & etc. :)
Link to a younger couple who have done what my friend and his wife are thinking of doing:
THE BINGE STARTS HERE! Sailing Zatara Adventure Episodes
https://www.youtube.com/watch?v=1D0AcIiKxzI&list=PLOXANRYEQcA1qEAavxmORqF-h3Z05SlOZ