Shim6 is not 8+8; the address changes take place in the end system.There is not as yet any technical reason why this should be so.
No, but there's a whopper of a political reason.If we've either misread the politics or the playing field has shifted and 8+8 is now a politically tractable solution, we should definitely explore it. It is, architecturally, a much cleaner solution.
Tony