A few years ago BMW started such a scheme where you’d trade in your old battery pack against a new one for your i3. The old batteries would go to a second life, probably as power storage somewhere. However, BMW UK declined the offer to be included in this at the time.
Renault Zoe batteries were also upgradable & again the old ones were used for a second life in powerbanks.
The Nissan scheme for the Leaf only offers a battery like-for-like swap, so no increase in capacity, but you can buy an aftermarket 2nd battery that fits into the boot to increase the range.
If you open the battery packs in these vehicles you’ll find they are full of battery modules & the BMS, so you could swap out bad cells, or, you could change the battery cells in whole banks for larger capacity ones potentially.