We're in 32-bit land, though, does it make sense to allow multiple sets of PID parameters for multiple target temperatures? One per ten Celsius degrees, perhaps, or a maximum of five and it picks the closest? I don't know how short of EEPROM and code space the Duet is.

You can do the same thing with G10 P0 Z### to set up a Z offset, and G10 P0 to show the current offset. However, any change you make won't take effect until all moves alrready in the queue have been completed.

Amazing! One more reason everyone should upgrade to a duet.

@T3P3Tony:

Another option would be to add software PWM to any unused GPIO pin that can currently be used by M42 depending on the PWM frequency wanted this could add too much overhead though.

The overhead would be high unless the PWM resolution were limited to 1ms or the timing were done in the step ISR, which I would rather avoid because of the impact on maximum step generation speed.

Regarding deciding if a heater output is used or not, rather than a new M code, why not just allow all heaters that are not added to a tool to be used as PWM?

For safety reasons I would rather the user made a definite statement that there is no heater attached to the pin. But perhaps we don't need a new M code, we could add an option to M305 instead.

I second this demand, as for miscellaneous reasons, I have done the calibration many, many times.
What I have done yet to help is making a macro for each sensing point. This macro go to the given point 0.5mm above 0, so P0 go to point 0 X, Y , Z=0.5, P1 go to P1 point X,Y, Z= 0.5, etc. This help a lot compared to the manual move to each point.