But then there's the question of why introducing new photoreceptors is special in this regard.

Because introducing new signals from new photoceptors changes the network dynamics and leads to new concept learning.

And if this type of stimulus can't be produced by other means (like seeing the world through a special camera setup, like I mentioned), and, if so, if such other means could in fact produce novel color qualia.

From the information you provided, I suspect that the deuteranomaly case is functionally similar or equivalent to the bichromatic case. What really matters is the actual connectivity structure of the gabor filters in V1.

if so, if such other means could in fact produce novel color qualia.

Well, theoretically you could add even more chromatic signals - for infrared say - and if V1 rewires to include those signals, then the patient would report a new infrared color qualia, of a type no human had experienced.

On a related note, there is a wierd experiment involving a device that encodes images onto the surface of the tongue, allowing blind patients to 'see' the output of a camera through their tongue. That could be considered a new 'qualia', as the resulting visual pathway is undoubtedly quite different than normal.