I have searched the internet for the answer to this, and to my surprise, there isn't a lot of (specific - YouTube tutorial, etc...) information regarding this.
 
1) Can a standard DVD display 21:9 aspect ratio?
2) Can a PS4 display movies in 21:9?
3) If not to both above, how in the world do I watch 21:9 aspect ratio movies?
 
Thanks for responding if you know the answer to this!

Scarlet-Tech
Wait... is this another new monitor? I don't have an answer, but I am going to poke fun at your monitor habits.

Ha ha - Poke fun at how bad I am at RETURNING items
lol - Newegg Premier hates me.
 
But I really found a keeper
 
I love this BenQ Xr3501!!!
 

so I did some experimenting with my Dell UW and my Xbox One. Short answer is NO :(.
 
You cannot enjoy a proper experience with a UW monitor and Xbox One for blu-ray playback. I did try and force the 21:9 aspect ratio and it looked terrible. The screen was stretched and it lost its aspect ratio.
 
You need to have a PLEX server(I use FreeNAS) with a computer(Windows 10) and stream it thru the PLEX (browser) to enjoy it properly. At least, this is the only way I know. As long as the Xbox controls the resolution, all the apps within its OS are limited.
 
Hope this helps. I had to unhook my monitor and lug it 20ft into my living room!! :)
 
The Martian 2.4:1 - this is close to the 2.33:1 ratio of the monitor

 
Avatar 1.78:1

 
I realized, that I should have also used the PLEX app on my Xbox to see what it would have done. I wish I would have realized before I moved my monitor back!?!?!?!? errrrr

I moved my monitor back to the Xbox to see PLEX on the Xbox One vs PLEX for PC. I also wanted to show you what the "forced" 21:9 ratio does. Now I am done. 
 
 
EDIT - I will add that if you acquire a movie in the 16:9 aspect ratio or any other, it will stay in that aspect ratio on playback for PLEX. PLEX does not change the aspect ratio to 21:9.
 
Auto Setting

 
21:9 "forced" setting

 
PLEX on Xbox One

 
PLEX on PC

 
 
 

 
you need to run PLEX on a computer first as a server. The computer can be a windows machine, FreeNAS, or any of the NAS boxes can work as well. PLEX is designed to stream your media to multiple devices. If you are not streaming and all of your files are local, then just use VLC media player.
 
 
here is the site for plex. It is not a simple thing to just setup unfortunately :(
https://plex.tv/
 
 

I used to use ArcSoft Total Media Theatre to do this on my 21:9 display (when I had one)
 
Its recommended by Nvidia http://www.nvidia.co.uk/object/3d-blu-ray-software-players-uk.html 
 
Use automatic zoom from the aspect ratio menu