> I think IPv6 should have been 8 bytes instead of 16

You don't state why you think this, but this is almost always due to the flawed thinking that the IP address is a simple identifier, and then looking at "how many IPs does the world need?" → "64 bits is enough". (IPs are like street addresses, in that they're routing instructions. Having the space not fragment — like v4's space is doing — is part of it, and helps things like routing tables remain small.)

> and somewhat backward compatible with IPv4.

The pigeon-hole principle makes backwards compatibility impossible. No matter what concrete scheme you might propose, it is effectively equivalent to IPv6.