As for fires, presently not much of an issue bar the immediate issue of a burning car, but presents a problem should the batteries remain as is when there is a time when most cars on the road and large car parks are EV - it would be better if the industry adopted better batteries sooner rather than later rather than count on further income generated when the owners eventually move to a better battery configuration. eg [1]
Toyota has a 6 stroke, sorry I missed that. I follow such engine improvements with interest, but not so much since a 8 stroke was developed and news of it buried. (It was a test bench only engine, and didn't need additional cooling, said to be 225% than standard engine) Sadly I'm unable to find any additional information on it or the Toyota 6 stroke, but then again when I went decided to also look for details on the large 6 strokes that were used for power generation, one such large engine I'm sure was mentioned at length at wikipedia - it too seems to be yet another entry, that's been cleaned up and mention of it dropped. [2]
[1] https://hub.jhu.edu/2019/10/17/lithium-ion-battery-safety/
Yep, people tend to calculate EV emissions all the way from the "child miners of Congo". For ICEs they just grab whatever the manufacturer reports coughVWcough