I recently ordered some 3D printed keycaps from
Shapeways to get a feel for what they're like. I gotta say, their "Strong and Flexible Polished" plastic leaves a lot to be desired. From a novelty standpoint they're fine, and especially for the price it's hard to complain (most are just $5-10), but they've got a ways to go before competing with artisan keys.
I recently found out there are 3D printers that can do multi-color plastic blends, but they're very expensive to own so not many of them are out there. In the future once 3D printing evolves to be able to do higher quality plastics in multi-color en masse, I think we'll see some really awesome stuff. Particularly, multi-piece designs that require exact precision are something I'm looking forward to. There's a 3-piece astronaut keycap below.
Here's a longer write-up of my thoughts with some more photos.