Could you make a display with 4 subpixels and 4-primary color space?

[Qbcd]

If you wanted to cover more of the CIE 1931 color space, could you have 4 primaries instead of 3, so you get a rectangular shape that can cover more of the space. And then you'd need to make displays with 4 subpixels, they would be RGB plus another shade or green that is sort of a teal color.