said by aaronwt:
1080P (1920x1080P) is considered 2K. Even though it's not quite at 2000 and only 1920. Just like the 3840x2160 resolution of UHD is considered 4K even though it's only 3840 lines of resolution.
I was making the differentiation on aspect ratio, but yes, 1080p is technically 2k.
The point still stands though. Most feature films since around 2000 have been using 2k digital intermediates (especially when special effects are involved) and the practice continues even today depending on budget. Those movies, even with a 4k master, are never
going to benefit fully from a 4k display unless the movie goes back to the source 35mm footage and is re-edited and gets re-created special effects (if there are any.) They will be barely better than the 1080p blu-ray copy otherwise.
Older movies that were edited on film can be easily re-scanned at 4k, but there's the question of how many are going to be done.
Let's face it, the only reason why we have blu-ray copies for some movies is that they did an HD master when they did the original DVD release. It's very unlikely that the studios are going to see the value in doing a 4k rescan of their back catalog for anything other than their top gems. It's just not going to be economically viable.