I started by collecting VCDs in my childhood and I've seen how things progressed over to DVD, dual layer DVD, then blu-ray etc. And now UHD blu-ray. 4K is going to be mainstream, sooner or later. In the pace that technology is progressing it would be sooner than later. Maybe in a couple of years. 2-3 years ago 4K UHD blurry was not really that popular of a thing, if I am not wrong. But now there are many titles and new ones releasing in UHD BD format.Thats exactly a nail on mah head man! Mine is the 2016 15" with full specs. Extreme buyer's remorse. T_T I am a designer too, OCD as ****.
A 4000$ MacBook Pro can't beat a 1300$ MacBook Pro (not mine, mine is a TB one) - just thinking of this would make one angry. But hey... not everyone has to be upset. This 4K media frenzy doesn't interest everybody. I watch stuff a lot, so it becomes a big deal to me but I know a lot of people who could care less about the resolution of the movie they watch. People started crying when they removed the SD card slot saying that the "pro" people can't use it anymore. It might be issue for some people, yeah but certainly not for everybody. There are many other professions where the "pro" people don't use their SD card slot AT ALL. Things can be like that here as well. People who are not super into high definition stuff, 4k isn't a matter of importance to them.
In your case, I know I have no place to say. But if I was in your place and I was very much into 4K, I would sell my laptop even if I lose some money and save me some frustration. But if I didn't have to think of 4K this much, I wouldn't think twice about it. A laptop typically lasts 5-6 years for most people. Your milage might vary. So do whatever reduces your worry.
One OCD designer to another.