So what sort of network would require a complete redesign for v6? I'm sure there's something out there somewhere, but it's not common. People that incorrectly think that v6 would require a complete redesign of their network are a lot more common.
> IPv6 does the job, but it is certainly not the best solution to the problem. If it were, we wouldn't have an uptake problem.
Your second sentence doesn't logically follow from the first. It's entirely possible that the best solution has an uptake problem.
As far as I can tell, it's impossible to make a solution without an uptake problem, and it's my humble opinion that being impossible disqualifies a solution from being the best solution, on virtue of the fact that we couldn't actually do something that's impossible.
To be clear, my basis for believing that it's impossible is that (a) current v4 doesn't support bigger addresses, (b) any method of upgrading it requires lots of people to do something, and (c) it's the "require lots of people to do something" part that causes the problems in uptake.
Lots of people think they have a way around one or the other of those, but their ideas always seem to be either impossible or already implemented in v6.
(As always, you could easily change my mind by giving me something that doesn't fall into one of those categories. But if your idea is "just add another octet" or if it involves pointing me to dozens of pages of draft text, expecting me to read it all and decipher your idea for you and then spend weeks dancing around explaining it to me when I conclude that you've just reinvented something that already exists and ask you to explain how it's different... then you're probably not going to have much luck.)