This is a good thing to ponder for a special niche: unprintable original art, where many of he colors used are outside the gamut of what can be printed with ordinary printing methods.
Of course, the tricks would be choosing the right palate, and featuring the unprintable colors in the right place in the image, and making them essential to the color composition. I think abstract painters might benefit from this. I know that metallic paints and gold leaf and things like that could work well in mixed media, with the same result.
On the other hand, not so good for selling on a POD site!