We already have v6 addresses that are semantically equivalent to v4 ones: ::ffff:a.b.c.d. You could put extra address bits into option headers instead of expan

We already have v6 addresses that are semantically equivalent to v4 ones: ::ffff:a.b.c.d. You could put extra address bits into option headers instead of expanding the address fields, but... what do you do then? How do you make things work? No existing OS, software or hardware device knows how to use them, and you have to go around and update those in exactly the same way you have to on v6. None of what you've suggested here would have allowed us to finish in the mid 2000s.