Another thing to be aware of is that most movie theaters using digital projection are still in 2K. I have no idea when 4K will rule the commercial digital theater projection space, if ever. So for the majority of theaters, a 2K DCP is perfectly sufficient. Right now, there's still no overwhelmingly large incentive for major Hollywood studios to be making all or even the majority of their movies with a 4K master. You have to remember that blu-rays/DVDs are a shrinking piece of the revenue pie for the movie industry, due to piracy, and perhaps streaming's proliferation. Maybe 4K blu-rays might breathe a little life back into physical home video sales for the short term, but who knows for sure what will happen in another 5 or 10 years?
An a different note, if you're shooting on 35mm film, then having a 4K film scan and 4K digital intermediate master is pretty beneficial if you're doing a film-out. If you shoot the movie in 35mm film, and then scan the negative dupe at 4K, then make an interpositive print, followed by several internegatives, followed by large amounts of release prints. Then yeah, scanning at 4K is a great place to start. If you start the negative dupe at 2K, then the image gets a bit soft by the time it reaches the release prints. Of course...how many theaters are projecting movies on film reel these days? LOL