I think that commenter meant that he wants to be able to separately declare physical and logicical layout of datatypes, and be able to assign multiple physical

I think that commenter meant that he wants to be able to separately declare physical and logicical layout of datatypes, and be able to assign multiple physical representations to a single logical representation, for different places they might be stored. I'm not sure how I understand how this would offer a benefit over just explicitly converting between identical logical representations with different physical representations, and it would definitely increase complexity.