There is in fact an options section in v4, and I think it's pretty obvious how it could be used: you could put extra address bits there. The problem is... how

There is in fact an options section in v4, and I think it's pretty obvious how it could be used: you could put extra address bits there. The problem is... how do you get those extra address bits to work? If you think through that question and produce a working answer, your working answer is going to be roughly the same as v6 -- and have the same issues v6 does. Almost as if the people that designed v6 weren't completely clueless.