@juanblanco
Moving ABI to SSZ will have a huge impact in general, not just at the calldata level, but 712, events, full frameworks (think mud) will need to be rewritten. All current applications will need to change, backend / frontend, and tested, and obviously rewritten in many areas. This might mean, that applications that target different chains due to compatibility might not upgrade and keep old formats. RLP might have a smaller impact if there are new transaction types that overtake others.