I haven't checked it since making this post, as it slipped off my radar becasue it lacked the option; however, you can play it in 21:9 only in Borderless Windowed mode, so try that. Don't quote me though as I only saw it mentioned in a video description box and haven't tried it myself
This was where I saw it: https://www.youtube.com/watch?v=jfBYQg8bFFQ
I did see posts in another video saying there is no true 21:9 mode that works flawlessly, as it crops a certain percentage of the image in this mode, and you may need to mess with the FOV slider to get it looking right. Interactions with NPCs and menus will also remain 16:9 .
I think I'll just pick it up for PS4 at some point and play it in 16:9 at 30fps with muddy textures and screen tearing. How hard can it be to include a true screen resolution option for a popular monitor spec, particularly for gamers?
I hope that helps .
Over and out . . .