I’d think for the vast majority of uses it’d be just fine. The duty cycle of a soldering iron is extremely low. Most of the time it’s sitting there topping up the heat on the iron, barely sipping power. If you’re truly cranking heat into some ground plane, a wireless iron is unlikely to be the correct tool for the job. Also, you could set the threshold for backing off the iron to be lower than “too hot to hold” if that’s a concern.