Re: IP8?
That's roughly what they did.
*Any* address size other than 4 bytes is going to break wire formats not only for IP but also for pretty much every transport protocol that goes on top, so 16 is roughly equal to 8 in this context. Then, having broken all other protocols (mainly in layer 4 but obviously also some address discovery protocols below and DNS stuff above) you have to specify exactly how you are going to repair them. So they did that, too, because they had no choice.
Another area where they had no choice was to produce *some* sort of 4-6 interop and (would you believe it) they did actually try the obvious solution (a special 12-byte prefix means an IPv4 address) suggested by three or four commentards here. Sadly this turned out to have issues and even if it hadn't, *any* interop solution requires changes to the IPv4 stack as well as the IPv6 one, so you are still faced with the question "How many times do we want to change the length of an internet address?". (Clue: the answer is "Zero, but if you put a gun to my head I'll do it once and fix everything whilst I'm doing it because there's no fucking way we will ever get this chance again.".)
Beyond that, the extra guff in IPv6 is a load of security which is optional but increasingly implemented in IPv4, some working multicasting which is again optional but almost universally supported in IPv4 routers, and zeroconf LAN configuration, which turned out to be such a good idea that people have tried to reinvent it for IPv4.
So I'm struggling to see what the problem is.