While that was true with the first few years of 4K tvs and a way to upsell to them that's really not the case now that we have actual connection standards and the hardware that meets those requirements is in the tvs. Hollywood will be doing more and more in 4K and 8k as time passes, many are already there. Unlike 3D which was a tangent and needed a parallel processing 4/8k is linear and doesn't require any real additional steps to creat. In fact it's easier in some ways and simply running it through a down converter to Hi Definition is simple. 4K is coming. It will come from every path except over the air IMHO in about 5 years with a decent amount content since there is already a lot of content being produced in it now. It's just going to be a few more years before anyone has adequate way to get it to a customers home. One exception is DIRECTV. They are about the only ones who could launch several channels in short order. Short order being tomorrow.
With that said I expect a 4K appletv within 2 years. I think they will want a good App Store first and see if they need to tweak anything before going that route. The big thing is also hvec decoding in the home device. That would have required a larger box and if you wait another year or two it'll be able to be put in something about the same size as the new one is today.
The question is, why?... we're going to up our stuff to 4K just because we can? Upping the source material almost always makes sense (within reason) as you'll end up with a better edited end product. But, if you can't tell the difference at the display point (i.e.: most of the current selling 4K TVs in real-life environments), it's kind of a waste (i.e.: downsides for no reason).
You might be right that it's going to happen, eventually... but it might not be a bad idea to question whether it really should happen. The trend I see seems to be more towards people watching content in their own personal ways on small screens (i.e.: mobile devices). One of my friends, the other day, even told me he thinks they are just going to get rid of their TV. Homes will probably get smaller with less space. And, I don't think most people get TVs over 60" in size... even if they can afford them. IMO, it's more like a solution looking for a problem.