Just when computer started handling 1080 HD like they used to handle SD, here comes 4K to mess it all up. Ok, if you have a machine made in the last 2 years or so it'll probably muddle through 1 or 2 streams of 4K all right. However it probably won't do so great with several. I know, we aren't always doing several layers of live video, but sometimes you do. Sure you can play 1 4K stream ok, even through on maybe one color corrector or scale / position and you get through it. That may be good enough for a while but eventually like in the start of the HD era you'll want better performance. Some how the newest machines with massive internal bandwidth to push the image data around are going to matter. However, I think you could easily stretch out at least a year before needing to take the plunge.
Wait, what did I just say ? Yes I think 4K is going to get shoved down everyone's throats and you'll have to do it. Consumer demand for HD started slow but then took off at a pretty steady rate to where we see 70-80% of the viewing market now has at least one HD set in their home, or computer screen. While 3D surfaces every decade or so and tries to become the standard but flops ever so badly, 4K is different. Its the next HD and it will come because it will. Its going to have far more marketing behind it because bigger is always more marketable. 4K panels are already out with prices that are acceptable to mid or upper end consumers. If you are going to spend $800-$1200 on a new set, will you buy a 1080 or 4K set for the same money ? in CONSUMER land the answer is 4K because, well its better, right ?
As a pro, you'd look at other things like contrast ratio, 6bit vs 8 bit vs 10 bit panel, color profile and adjustment, local LED dimming, and other features that mean a better more accurate picture over just the shear number of them. Another words you are looking at the quality of the pixels ! most consumers aren't outside of the stupid worries about refresh rate which is mostly bogus past 60hz, certainly past 120hz where a pixel can turn on or off in 1/2 a frame refresh so there should never be lag.
Let me also say, I've seen native 4K and its amazing. I've also seen 8K which makes 1080 look like SD. There are days when 1080 just isn't enough for me, it looks a bit soft and lacking detail at times. This is especially true when you start to get closer to the screen.
What this means quite simply is this : if the material you are shooting has any future value or life, say 5 years from now then 4K is something you need to get serious about now. Start figuring out what work you are doing or expect to be doing this year for which 4K will have future value. Nearly 10 years ago I saw HD coming the way it was. While many productions where shooting SD I was selling HD. My marketing was simple - is what we are shooting now going to have future value ? In almost all cases it did and I still pull shots from those shoots back then on occasion when I need them. While I decided on 720 back then, they scale up into 1080 just fine now with PP's high quality scaling. I made the 720 choice back then for a number of reasons : almost all HD sets where in fact about 720 in resolution, it looked great in SD deliverables, my G5 mac tower easily was able to edit it - 1080 was kinda of chunky at that time, storage requirements weren't as high, it was just easier to handle all around. Another factor was that the first affordable HD cameras at that point were also 720 - HVX-200's, JVC HD100/200/250's. I jumped on the JVC HD-100, shot a lot of great material with it and switched over to dslr's a few years ago. Its funny how I looked at the dslr material vs the JVC and saw the dslr material looked better, but now I do the same thing with my C100 vs everything else past.
So my words of wisdom are : don't ignore 4K. Its coming, plan for it, find clients and projects for which its appropriate and get into it in a carefully planned way that doesn't leave you broke ! Also know when HD is just fine. Don't just go and sell 4K because you have a camera that can. The back end of editing / storing / achieving is very significant. Its also fair to say that 99.9% of the projects viewers will never see it in 4K for now, but maybe in 5 years they will. Take that into consideration as well if the project you are doing has a shelf life of a year, you don't need 4K for that ! Be wise, smart, careful !