Re: Bad assumption on some of the proposed solutions...
"There's next to nothing that can be done about such internal short circuits, except to invent some new-fangled self-limiting or self-extinguishing action within the cell materials."
How about a powerful disruptive charge to blow out the fire? After all it works on oil rig fires.
Seriously though, perhaps a coating inside the casing that will in the event of a short and overheating that ruptures the casing, will react to produce a rapid self hardening foam sealant to rob the lithium of oxygen .