I can confirm this! Here is a quick screenshot of the demo land battle in 3840x1024:
Would take more screenshots, but doing PrintScreen + Copy and paste into Paint is annoying, is there a hotkey in game that makes a JPG?
Taken on default graphics settings (either Low or Medium, I forget). The UI is perfectly center in the screen, and the FOV looks normal Hor+.
The only thing is the main menus are "centered widescreen" so an inch or 2 on the left/right monitors is visible (not a big deal), and the intro movies are all stretched (or zoomed in Vert-? didn't bother paying attention).
Hopefully the main campaign map gets treated with the same attention, because I'd love to finally game Total War on my 3 monitors!
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This just went from a "maybe buy right away" to a "must buy right away"! Creative Assembly is truly the king of strategy games.