Re: "We have now run out of IPv4 addresses"
Transitioning quickly away from v4 wouldn't make v4 forwards compatible, it'd just take us off of the incompatible protocol quickly (which would avoid the problem, sure). I don't think you could've done that in 1995. Even 1985 probably would've been too late for that.
> Also that the only real difference was the length of addresses, with the leading 4 bytes effectively being padding and thus could be simply discarded or padded as necessary.
If the leading 4 bytes are padding then there's no point in them being there.