@William L Carman
I use the method of presentation you suggest.
Many commercial theaters no longer use masking as well. It is partly about having a projector with good black levels, (being able to stop most of the light when doing black) having a dark appearing screen and lastly conditioning yourself to when is good enough.
My screen is a total wall painted a .5 gain neutral gray. For years I messed around with 2way masking and then adopted a zooming method of presentation and started playing with 4way masking. Always thinking about wouldn’t it be nice to do what you suggest.
Last year I got a new dark chip 3 DLP projector that has a decent black level and enough lumens to do a CIH+IMAX size screen at 110” on my gray wall. I had family over for a showing of Dunkirk a movie with changing AR’s that is imposable to mask for. After the movie I quizzed everyone about the movie and if they liked the expanding IMAX parts and if they were bothered by the black bars during the scope parts. No one noticed any of this. Not even that the movie was changing between scope and IMAX constantly. To be honest I didn’t even notice 75% of the changes because the movie was so good and the viewing was quite immersive. I had to actually replay a couple parts to prove to people it happened.
This got me thinking and that 99% of the world is conditioned to not care or pay attention to what goes on outside the image as they are focused on the movie. It is just those of us that think about this stuff way to much that get bothered, and actually it ruins the movie for us to some extent.
I went cold turkey and said what ever faint black bars I’m seeing will go away when I quit worrying about them and they did. It is very freeing to just zoom too the size that seems right for the content I’m watching and for the most part I follow CIH+IMAX but I make exceptions for Academy AR movies and some of the new prestige streaming TV. I still watch DVD content even and due to PQ I run it slightly smaller sometimes.