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I'm also interested in what expanded color vision would be like, but it looks like that paper was describing one of the obvious approaches I'd already thought of. I didn't read the whole paper, but from the abstract, it looks analogous to one of the widely-used treatments for color blindness, namely a single red-tinted contact lens.
Many other vertebrates are tetrachromats. Mammals are unusual for being more color-blind. The loss of two types of cone cells is thought to be due to the nocturnal phase of our evolution when dinosaurs ruled the earth. Primates have since evolved a third kind again. Birds never went through this phase and are still tetrachromats.
A gene-therapy experiment gave color vision to color-blind monkeys. This approach could theoretically produce a fourth type of cone cell as well, but could they then distinguish more colors?
Some women may be natural tetrachromats, due to a mutation in a photopigment gene in one X chromosome, but not the other. It's not clear if the tetrachromat ability of certain women is due to ancestral neural pathways from when we were tetrachromats, but given the random way gene therapy works in the monkey's cells, it seems likely that neuroplasticity is enough. Given consistent "pixels" that react preferentially to certain colors, the brain learns to perceive them as colors. Thus, I believe it's likely that the human brain could learn to perceive a color gamut built from even five or more primary colors, given proper inputs.
The fact that sensory substitution works suggests a non-invasive approach. If you could track and target the eye well enough for a display to consistently change the color sensitivity of a scattered subset of retinal cells, it's likely you could use it to train your brain to not only distinguish new colors, but to perceive new color qualia.
The color processing system in the human brain is not that plastic. The higher levels probably yes, but the lower levels: No. Sure you can perceive and have benefits from these filters, but it's not exactly the same as having earch processing or luminance and chrominance built into your hardware.
http://www.allpsych.uni-giessen.de/rauisch/readings/Gegenfurtner.NatRevNeurosc.2003.pdf