I agree about Nissan's lack of motivation to support replacement packs but I also think that putting a Ariya pack in a Leaf would be a non-starter from a technical point of view. It's a new platform and probably has a completely different mechanical footprint. Then there is the addition of active cooling which the Leaf does not support, etc. Anyone in tech knows that retaining backwards compatibility is often a huge PITA. A new platform is often a new design from the ground up and trying to make it fit into an older, obsolete application is a huge constraint that has little or no payback. It would be akin to putting a Porsche engine in a Chevrolet. The number and scope of incompatibilities are enormous.