OTOH, I never had even thought of the blade of a light sabre being cold.
Yeah, that cold.
And like photons passing through one another without having any lasting effect on one another, photonic matter brings with it the ability to pass through regular matter like a knife through butter. But unlike photons, it has a huge effect; namely, rendering asunder that which it effortlessly passes through. The best of both worlds?
According to the original Star Wars canon, lightsabres emit no heat.