I think it would be pretty difficult to come up with some kind of three month course to improve the quality of your art (that is as productive as what happens in the real YC), but you could teach artists how to market themselves, I guess. Lots of artists aren't good at that.
I think it would work for artists interested in working commercially, to help them get skills for whatever field they wanna go into, learning how to market themselves, and getting connections. For fine artists who just want to show their stuff in galleries and museums, I don't know how useful it would be, besides the money.
What were you imagining for the "YC of art"?