Thanks, those were very interesting insides that I didn't have so far. Very useful!
So, it means that it is indeed possible to swap an old battery for a newer generation and that has already happened. It's very comforting to know that.
Again: I'm not worried about the longetivity of the battery itself. I drive electric cars for 4 years and know that this is not an issue.
I just wanted to know whether there is potentially a path to an upgrade in case one day, e.g., a 20 kWh battery is available.
Thanks again for all the replies.
While I'm not a Zero owner, I very much doubt there will ever be a supported upgrade path. There isn't one in car BEVs, even when it's technically possible: The Leaf's batteries from the original 24kWh through the 30kWh and the 40kWh one on the 2nd-gen have the exact same form factor & interfaces, and Nissan won't sell a Leaf battery except to an owner, and only the exact same one as currently in the car, upon proof that it's defective or seriously degraded: This is because of the global battery shortage.
It's not worth a BEV manufacturer's while to provide a battery upgrade path when they'd make a lot more money by selling that same battery in a new vehicle.
Also, replacement of car BEV packs is rare; there's mostly consensus the original battery will remain the lifetime of the car (as it slowly degrades, it'll just be repurposed as a shorter-range vehicle).
This is even more true of BEV motorcycles, where AFAIK the battery makes up a higher % of component costs than it does in BEV cars.
It's also not going to be worth it economically to the motorcycle owner. If within the warranty period, replacing a fully working battery means throwing away a large investment (esp. since AFAIR, a non-warranty replacement (e.g., accident) is typically only guaranteed for a year); by the time the 5-year period is over, the bike itself is only worth half as much as it was when new, and the owner is unlikely to recoup the investment.