I wish I could help you, but I don't have such fancy monitor to test. Theoretically, the game should pick all available resolutions on your monitor, unless maybe there is some hardcoded limit how much resolutions it goes through before it stops or there is some other issue I'm not aware of. Can you tell if the game offers all other supported resolutions except 3440x1440?
I haven't really changed anything regarding resolutions since it seemed the game picks all of them by itself, at least for fullscreen mode, which is probably the preferred mode by most people, I just added the code that sets larger field of view, depending on selected resolution's aspect ratio, so this is definitely an interesting issue.
And there's the fact that nobody with skills is interested in hacking this game, I'm an amateur when it comes to these things, I guess it was luck that some bugs I've been able to fix or bypass in some way were so obvious. The absence of game's source code only makes things significantly harder.
"When a human being takes his life in depression, this is a natural death of spiritual causes. The modern barbarity of 'saving' the suicidal is based on a hair-raising misapprehension of the nature of existence." - Peter Wessel Zapffe