Not only is it open source, it's free software! I am very pleasantly surprised to see that the GNU GPLv3 license has been chosen. I've been harsh on Light Table because the source was nonfree and the promise to "open source" it eventually didn't look promising or community-friendly. I expected a permissive license or an open-core strategy to monetize proprietary components and not be friendly with the free software community, but that doesn't seem to be the case here. I look forward to seeing where development goes.

Happy hacking, Light Table devs.

That's not correct. The resolution you are referring to is the native running resolution of 4K projectors in cinemas established by DCI. If you were being legal about it, which your comment is a little bit, "actual" 4K is 4096x2560.

A "proper" 4K film shown at DCI resolution is cropped by removing lines due to the combination of aspect ratio between film and projector. The trend in film photography, however, is towards the DCI standard; the RED EPIC shoots at DCI 4K while its predecessor, RED ONE, shoots more lines (I cannot recall off the top of my head, but it is definitely larger than DCI because it didn't fit in my Media Composer DCI workspace the first time I worked with it; I'm really reaching in long-term memory so I might be wrong about this).

All of that, however, is in the cinema world. Since NHK demonstrated 4K TV a couple years ago, everybody in the consumer electronics world has understood 4K to mean 4x 1080p, arranged 2x2, and that is what ITU standardized in recommendation 2020. That's intentional.

It's much easier to evolve 1080p equipment to 4K TV than cinema 4K; it's multiplicative and most of the same equipment can be overhauled. Other resolutions affect aspect ratio, and lenses are a significant portion of the expense of a television camera. You're going to have a hard time selling a standard that makes everybody buy lenses again. Don't forget that everybody just did to go HD. (The last lens I shot on in news was $20,000 by itself, which is part of the reason the average photog will get really mad at you if you grab it, as people who don't want to be videotaped are wont to do.)

If a consumer is buying 4K equipment, its resolution is 3840x2160. This will also be the resolution at which 4K content targeting consumers should be encoded, so I'm not sure what cropping you are referring to. If a DP is buying 4K equipment, its resolution is higher. This isn't marketing droids winning, it's completely different industries having a different history of resolutions: DCI 4K builds upon DCI 2K as 4K builds upon 2K builds upon 1080p; cinema has always fought for 16:10 while consumer electronics stubbornly fight for 16:9, as well.

Wikipedia doesn't help this situation by blurring the history of the two, leading to comments such as this one. Cinema 4K and consumer 4K are not in competition with each other, and there was never a chance of 4K content coming out of the camera at 4096x2560 and making it to a consumer display. They're for different purposes. It's also worth noting that ATSC v3 is still in early stages and is not finalized, which will dictate the broadcast of OTA 4K TV content and pull the industry accordingly.

I am aware some 4K monitors have been released to market at cinema resolution. Those are targeted toward film editors and as monitors for shoot work. There's also some other crazy markets; an engineer I worked with in television installed a bunch of early 4K monitors, the ~$20k ones, in an air traffic control tower. They like the resolution because screens get busy, he said. I don't know if that's true, I merely remember the story.