Nope, not happening.
The very vast majority of people can't stream 4K at a worthwhile bandwidth. Heck, most people can't even stream 1080p without heavy compression. Apple has only just started offering 1080p streaming and it's nowhere near Blu-ray quality, but that was to be expected if they wanted people to be able to stream it. Now people should be able to stream 4x the pixels while the average Internet bandwidth has stayed the same?
The effect of 4K on a movie is more subtle than the jump from SD from HD was, and also more subtle than the jump from a regular display to a Retina display (considering you're displaying a lot of high-contrast vector graphics like text and other sharp UI elements on a computer/phone). In a movie, contrast is never as high and sharpness is often ultimately limited by the lens used to capture footage. You'll often notice several elements in a scene are slightly out of focus because of the depth of field.
Having seen 4K TVs in person, they look awesome but the resolution part isn't mind-blowing. You really have to get into big TVs (60"+) to notice it at average distance. The sharpness gain you get from the resolution would totally be negated by heavy compression artifacts if you were to compress 4K movies to the point they can be streamed by most (10-15Mbps). For reference, a 1080p Blu-ray movie is around 35Mbps, so obviously quadrupling the number of pixels while reducing the bandwidth significantly isn't going to look to good.
So yeah, who's willing to drop $5k+ on a 4K TV which's image quality wouldn't be better than a much cheaper 1080p set because there's no proper way no distribute 4K yet? If Apple had a plan to instantly become a high-speed ISP like Google Fiber it could work, but I highly doubt they're willing to make such an investment.
After all, we're talking about the same company who sells songs in 256kbps in 2013, and dare call them "CD quality". Even if people were ready for 4K (they're not), Apple would probably be too cheap on bandwidth anyway.
