We had sort of a preview of what to expect this week with the fatal Tesla crash in the Netherlands. The battery pack split open and shorting batteries caught fire on the road.
This would be an issue with a 787 crash today, but more batteries would mean a more serious danger.
As opposed to all the burning jet fuel? I'm not really convinced that the batteries represent an additional danger on top of the jet fuel, except for the fire department not having established procedures for handling it yet.
In the crash you referenced, the article I read said that the damage to the cabin from the fire was minimal and that the fire only really affected the situation in that it delayed the rescue folks getting to the driver (who I suspect may have had a heart attack to start the whole chain of events and was likely already dead.)