I'm sure you know this, but as an addendum, the majority of films shot digitally have been filmed with 2K/1080p cameras. Obviously there are exceptions and also modern, effects-heavy films might have their compositing done in 4K, so I'm not saying there's no benefit to going over 2K. However, in many cases you're already getting the intended picture at 2K and upscaling is not bringing you any closer to the filmmakers' ideal presentation.