I want to preface this post by acknowledging that these problems are a niche issues, not a lot of people will have these kinds of displays so not a lot of people will be encountering them. But they are still bugs that worsen the experience for people that do have these displays, so they deserve to be reported.
Character select
Characters are hard to view in character select compared to 16:9 resolutions, legs/feet get cut off on all characters, hands on asura, and heads on charr and norn.
Character creation
Similar issues arise during character creation: Heads get cut off even for humans, the painterly races and genders get cut off too.
Cinematics
Cinematics also have awkward framing, some suffer more from them than others however. A few examples: (spoilers obviously) Darkrime Delves cutscene, Heart of Thorns logo at the end of Point of No Return, Point of No Return again, All or Nothing cutscene, Daybreak cutscene, very blurry A Star to Guide Us cutscene, and a lot more in this album. I recommend comparing it with the cutscenes on a 16:9 display because some might not seem like they're impacted too much, but if you compare it to how it's supposed to look it's far more obvious.
Interestingly I did notice that a lot of the core game's cutscenes do NOT seem to have this issue, examples again: Intro cutscene for humans, first instance for commoner humans. In these cases there are actually black bars on both sides, which is MUCH preferred IMO. I'd rather not use my screen's full width over these framing issues.
Side-by-side cutscenes
While the normal cutscenes are fine in the core game this is definitely not the case for the side-by-side cutscenes/dialogues. These are actually much worse as the backgrounds become even more blurry and heavily overlap with the subtitles and skip buttons while also awkwardly framing the characters. Examples: Human cutscenes 1 and 2, charr cutscenes 1 and 2.
Mission completion emblem
This is a smaller issue, but fairly glaring: The emblem when you complete a mission/story step is oversized, see here.
World map
The world map becomes very pixelated when you zoom in, and very quickly swaps back to a painterly view even when you're not zoomed out too far.
UI hard to use
This is less of a bug but more of a note on the UI in super ultrawide: The static elements of the UI really feel too far spread out, chat is easy to miss and squad/party UI is hard to keep track off during fights. The latter of which really makes healing and keeping track of boons quite hard. I imagine this will be especially noticeable when trying to play the upcoming spectre on such a screen as it makes it hard to quickly select the right allies through that part of the UI to support them.
I've recently played other games like Halo: Infinite and Forza Horizon 5 which both have options that allow you to limit how far your UI spreads out over your monitor, a padding that pushes your UI further towards the middle. An option like that would be great to have here too, I think even people without these monitors would appreciate that kind of UI adjustability.
FoV weirdness?
And lastly there seems to be something weird going on with the FoV/when you turn your camera. Everything on the edges look very stretched out. See these npcs for instance, 1 and 2: looking right at them they seem fine, but when they're at the edge of your screen they're all stretched out.
An even better way to show this is this recording: https://gfycat.com/cavernousfamousbluebreastedkookaburra
Here you can see that the screen warps all over the place.
To be specific, this is on max FoV, the way I always play the game because it feels nicer to play and also gives you the best view of what's going on. This issue actually gets worse the further you zoom out, for example this is the same room on min FoV, and this is on mid FoV. As you can see, no/minimal warping on min FoV, and light amounts of warping on mid FoV.
I imagine this is just the way FoV works in GW2 and it would require a lot of work to fix it, but I thought I'd just bring it up. Main issue this behaviour brings is recordings and screenshots looking less good than they could be on this aspect ratio.
Main reason I'm bringing these issues up is that I'm worried that my experience of End of Dragons will be hampered by playing on this resolution. The cinematics being a main concern of mine though I'd love to see it all addressed of course. I hope this information helps!
Also again, I acknowledge that all this is mostly first world problems/luxury issues, and yet I think it's good to report it anyway as it does influence at least a part of the playerbase.