This was discussed in another thread
a while ago, although there was less urgency then. One of the things that came up was the proprietary nature of the battery controller and the VCM. Both of these computers must speak the same language for the pack replacement to work. One of the reasons for the lack of a 6 kW onboard charger upgrade was the new revision of the VCM, and other changes in control electronics in 2013 LEAFs, which would make the replacement cost prohibitive on older vehicles.
I like the effort around adding another 3.3 kW charger to the car, and keeping the same hardware. Interestingly, the OBC in the ActiveE consists of two 3.3 kW charger in parallel. So even OEMs can use this approach. Based on the old thread I mentioned above, the best way to approach pack replacement is to find a manufacturer willing to build cells with similar characteristics and identical form factor. Then reuse the existing hardware and computers to build a remanufactured pack. Depending on the condition of the cells pulled from the old pack, they could be likely re-sold for second-life applications.
The remaining questions here are: is it necessary to match the nominal capacity and the voltage curves of the original AESC cells? Will a battery controller be available for purchase and if not, can it be reverse-engineered?