Re: What about IPv4?
Yes, I get that's what you're saying.
What I'm saying is if IPv4.5 addresses look like IPv4 addresses a lot of software will break because of the bad assumptions it makes.
By making IPv6 addresses look completely different, poor parsing algorithms will more likely fail immediately instead of partially working and then failing for some other reason. (Like not being able to connect to a non-existent server because the address was only partially parsed.)