I miss two safety features in the teacup firmware: (don't wanna see a meltdown here)
- Something like Marlin's HEATER_0_MINTEMP
- Dual thermistor, measure difference between them
If thermistor reads below, say 5C, or two thermistors does not read approximately the same : shutdown
Without having much to back it up, I think the first one should be super simple to implement. The second one might require a little more.