And that is a problem Boeing will have if this ludicrous 'stronger box' solution is even considered by the FAA.
It is quite easy to force a problem by overcharging a battery or to try to charge a seriously depleted one but to force a thermal runaway due to an internal short circuit will be almost impossible to do short of manufacturing a faulty battery or charge/recharge cycling it until dendrite growth becomes a problem.
This all has to be done in flight too so that thermal effects on the rest of the electronics bay can be measured as well as the efficiency of any venting system.
The 'bigger, stronger blue box' solution may be a quick fix but I can't see proper certification of it being particularly quick. An alternative would be a mathematical extrapolation of the worst-case scenario based on the total energy inside the box but I really don't think anything short of a battery on fire on an actual flight will satisfy the FAA this time round.