Amazon's original content is coming in 2014, and it is all going to be shot in 4K. You'll definitely need a 4K TV by then.

Amazon plans to deliver 4K content, and has already produced five comedy series, - Alpha House, Betas, Annebots, Creative Galaxy, and Tumbleleaf—and there are five drama series on the way as well. All of them are getting the 4K treatment in the new year.

[Amazon]