Why no 4K 3D?

[man_westooth]

Is there a technological constraint that prevents this? Originally, I thought that manufacturers were just trying to get 4K players out quickly and had not yet worked through the 3D part. But the players have been out nearly a year, and I haven't heard of any fix for this. I'd like to be able to buy 4K 3D movies, but if I have to choose, I'd rather watch 3D on my upscalable 4K TV than a 2D version in 4K.