Heat increases with the mathematical square of the current, and so far the 40A charging current is the only known current that has melted some plugs. The next size down (30A adapter, 24A charging) would generate only 36% of the heat of the 50A adapter at the same resistance. That's not to say that there couldn't be a thermal fault on another adapter -- leave the screw loose on a 30A outlet and it will heat up quite nicely. But in terms of the "recall" it's Tesla will not have to replace them.
(In time, I expect that Tesla will re-engineer them all to place thermal fuses inside, just for protection's sake.)
I had questioned my service center on Wednesday about when the replacement plug would arrive, I returned home to find this on my doorstep. I went ahead and got the undercarriage retrofit for my Model S, and can drive around feeling that much more secure with this great car. The 14–50 replacement came via FedEx. I'll save them the return shipping and drop it off at my local service center (8-minutes away, near LAX). Plus I can have a great cappuccino from their new coffee machine (aka. Sarah's coffee machine).
I hope they've got their parts department set up because I hear they have some pretty cool swag like this new key fob protector:
It's made of a thicker neoprene than the aftermarket fob protectors I bought, which subsequently fell apart. There they go again! Tesla raising the bar.