The problem with replacing individual cells is you’ll end up with cells with different wear levels which means different discharge rates and capacities (max voltage). The battery management system can mitigate some of the problems that arise but can only do that while chargering. While the battery is in use or sits for an extented period of time the cells will try to level out the voltage difference causing loss in capacity and a potential fire risk if the cells are too out of balanced.
Replacing the battery with new better batteries isn’t really an option either as any significant increase in power density would be from a change in battery chemistry and that would also require changing out the on board charging circuit and related systems. There’s also the issue that the majority of charge points providers state in their TOS that the use of any aftermarket parts or modifications to your battery or charger is forbidden so you are essential blacklisted from using any DC fast charger.