New IPv4 addresses are being allocated at a rate of 6-7 per second and there aren't very many left. In a while, we're going to run out. What then?
I think that when it happens, some people will try to buy other people's IPv4 addresses, but frankly I doubt that there'll be enough willing sellers to supply 6-7 addresses per second, so at least some people will have to make do with only IPv6 addresses. That's going to be painful.
That period will be less painful if a few people put web sites and other services on only IPv6 now, so that the transition starts sooner, with fewer victims, and ramps up later.
I'm not willing to do all that much. But this blog is unimportant, so I put that on IPv6. I could have used a name-based virtual host or used one of my free IPv4 addresses, but someone has to make a start.
Later, maybe I can put something other than a web site on IPv6.