A couple of points. There are already restrictions on keeping chemicals other than ones that are used for domestic cleaning in units, so people don’t have complete control over what happens in their units. Lihtium ion batteries will spontaneously combust, but it is much less likely than other causes. The chances of it happening are greater when being charged, especially if there is overcharging, and when they are poorly manufactured. That is the big problem with some of the e-bikes, they have cheap and nasty batteries and cheap charging circuitry. The cars are highly regulated so problems will be rare.
I expect that the way this will work out is that if the insurance companies see a reasonably increased risk, then they will be telling government that either the price of insurance will increase or there need to be more rules.