Setting the device at 3.0V means that with the additional diode that should be in between it and the thermistor signal, you should get at least 3.3V, and at max 3.6V (depends on the forward bias voltage of the diode of course).
From what I remember seeing, 3.6V is within the Due's max input voltage range. This way we should get full scale readings with protection for the Due from higher voltages.
Regarding the Mega, you would want to do the following:
1. Use additional headers to provide more height. This means either you'd want to use longer pins, or you could use a bunch of stackable headers to extend the existing board.
2. With the thermistor circuitry, you would need to adjust the voltage divider resistors on the shunt regulator so that they're set for 4.7V, rather than 3.0V.
Both of these things are not insurmountable, but most likely can't be done by your average Joe. If we document it all, and point out the issues, then people will at least know what to do if they want to go down that path.
IMO it's not recommended using it on a Mega unless you ABSOLUTELY know what you're doing.
Note: The USB connector on the Mega is annoying even with RAMPS. Admittedly you can at least cover it with tape, but it's still annoying. I'm quite surprised there aren't more Mega clones with a MicroUSB connector. I only know of one off the top of my head, but it also has on-board Ethernet.
From what I remember seeing, 3.6V is within the Due's max input voltage range. This way we should get full scale readings with protection for the Due from higher voltages.
Regarding the Mega, you would want to do the following:
1. Use additional headers to provide more height. This means either you'd want to use longer pins, or you could use a bunch of stackable headers to extend the existing board.
2. With the thermistor circuitry, you would need to adjust the voltage divider resistors on the shunt regulator so that they're set for 4.7V, rather than 3.0V.
Both of these things are not insurmountable, but most likely can't be done by your average Joe. If we document it all, and point out the issues, then people will at least know what to do if they want to go down that path.
IMO it's not recommended using it on a Mega unless you ABSOLUTELY know what you're doing.
Note: The USB connector on the Mega is annoying even with RAMPS. Admittedly you can at least cover it with tape, but it's still annoying. I'm quite surprised there aren't more Mega clones with a MicroUSB connector. I only know of one off the top of my head, but it also has on-board Ethernet.