After spending a hefty bit to customize a mechanical keyboard the way I like...
Sure, I'd spend on an artisan keycap if it was related to my interests. At this point, it'd just be the last bit of personalization one can do to a semi-custom keyboard short of paying a pro to paint or hydro-dip the keyboard's case.
The next frontier to select artisan keycaps really, are full artisan key sets, where your keyboard is basically a miniature world stretching from the tilde key to the NumPad Enter. I could see companies paying for limited edition artisan keysets; Blizzard doing an Alliance vs Horde set, Alliance on the left, Horde on the right, and tiny miniatures clashing in the center. Limit the special boards w/ artisan sets to say, 20 as prizes. No one set the exact same; featuring different characters and equipment on both sides fighting across the keys.