in the event the bad guys find a way of making sure they do go into thermal
Forcefully bending or crushing the device will most likely cause enough damage to the battery to persuade it to short out and catch fire. No complex manipulation or computer skills required.
However, such fires are easily dealt with by cabin personnel as has been pointed out earlier in this thread. I'd dismiss the threat of a "bad guy" trying to bring down an airliner with his smartphone battery as "not very credible".
As for eventual attempts to have a device cook off while in checked luggage in the hold, I understand that most airlines already have a policy that dictates such devices be carried in cabin luggage only.