A lot of UO's graphics were made in 3D software (the characters, monsters, namely) and the overall style isn't that hard to reproduce. UO's art style was a big influence on me when I went into making my own graphics for a living:
I've got a huge library of graphics, though whether or not they would fit the UO size constraints is another story. I suspect many of them would, but a number would require resizing or alterations. The bigger hurdle, at least for me, would be creating the modular walls and roofs (roofs more so, though there might be some wonky engine thing UO does with roof textures to handle that).
A few more samples:
An example of some paperdoll stuff I made (I am big on making modular characters and pieces):
Another big thing is that you can't really just replace some of UO's artwork. Either you replace it all or you don't. When you start mix and matching art styles, it creates a visual inconsistency that sucks. Just look at the later stuff that was added to the official UO servers, made by completely different artists and it is obvious (and horrible).
I am not entirely sure what formats the images would need to be in for UO, but I suspect they are .tff images or whatever, so that would mean the graphics would not be able to have an alpha transparency layer (so no shadows, no smooth blending effects around edges, etc), which would pose another obstacle. It would be a very tall order, though not impossible. I am not surprised at all that Andrea would not be interested in tackling it!
one of the things is they were devoloped for 640*480. so as monitors advance (1080p, 2k, 4k) u basically get a super zoom version (classic uo).
with high res sprites you could create a higher def pixel sprite and make it continue to feel immersive instead of (birds eye is now helicopter view). also u can add a ton of detail to some areas (foilage/grass) and aging sprites (gazers, birds etc) or make cool sprites even more detailed (liche, drafons)
It is waaaaay more difficult to make the clothing and such appear on the avatar as opposed to the paperdoll. Making the paperdoll stuff is super easy. Making it for the avatar though, you need to make iterations of the same piece many times, for each frame of each direction of each animation. It's not really feasible I think, especially since it would basically be a project of passion that would take hundreds if not thousands of hours of work. Not saying it wouldn't be awesome, but with the amount of work required you might as well just make a new game entirely instead of remastering old artwork from a 20+ year old game.
For the record, I do love the classic style UO artwork. Even with its lack of shadows and such, it is still some pretty fantastic work. That is what makes it more jarring when there are monsters and such incorporated into the world that clearly have a completely different artstyle (a far more obviously 3D rendered look).
machine learning could be done in a week (processing wise) but it may or may not look good after updating to 1080p+ (basically increase resolution and upscale a ton). that would be a happy medium for now
I always thought uo needs less improving and more expandinf in graphics department. For example instead of increasing resolution I would bu much more happier to see more variety in the classic animations, such as lions, rhinos, giraffes on top of bears and crocodiles.
That is easier said than done though. If you do it the original way you'll need to produce animated geometry, extract frames at cprrect perspective and edit to fit color, contrast and edge strokes.
If someone adds a simple donkey to ride, as modest as a llama, he is my hero.