I'm making this thread basically on behalf of a friend of mine whom I convinced to get this game. The reason? Well, he's legally considered blind, to the point where he's only just able to make out the normal text in the game on a very large screen (70 inch). And since he's playing the game on PS4, there's no means for him to modify the .ini or add mods to the game to fix it.
 
Currently, however, he considering dropping the game altogether, since he is incapable of making out any small interactables, considerably hidden entryways (like the hatch next to Migo, for instance), and any items that are either tiny, or whose colour closely matches the background (even things like chests). To make matters worse, useful icons on the map screen and minimap, like exits/entrances and waypoints, in addition to the thickness of the border lines separating the playable areas from inaccessible areas, cannot be scaled (and don't scale on zoom) and thus he cannot make these out either.

What can he see? He can see the range indicators of spells (like teleport), he can make out the peace and combat highlights when set to full (not just circles), he can read the text (though he says it strains his eyes after longer sessions), and most of the UI.

Essentially, the necessary extra accessibility options that would make his gameplay experience playable narrow down to:
- An options to always highlight interactibles like doors, buttons, exits/entrances, levers, dirt piles, and visible chests, even when you're not within interaction distance (obviously excluding any non-discovered traps until you spot them). Since interactibles highlight when you get close to them, surely you could easily add a toggle to set them to be permanently on?
- Map UI scaling for: Icons, borders and text, in addition to normal textbox scaling. Since there exists a UI scaling option inside the .ini file, surely this could also be added with no large issues.
- Potentially an option to toggle on a permanent highlight of all accessible terrain (separating non-walkable from walkable terrain) - done in a similar fashion around the player as the teleport spell is indicated, so that it's easier to see where characters can, and cannot go. This could be done as a toggle-spell, showing the current range around the player as any other spell would - taking the range of, say, teleport.
-The option to make highlights thicker, and more pronounced.
   
The addition of these modifications would not only make the game playable for my friend, it would also make the game more accessible to any others who have vision problems, and still love cRPG's. I understand that proper implementations of accessibility settings takes quite a bit more time and effort than most people believe, but I do think that adding these additional options would make the gameplay experience for some quite a bit better.

Unfortunately, the UI is not very configurable, or moddable.
The UI scaling option is not applied to the controller UI, and even with the keyboard UI, after it was updated in the Definitive Edition to use most of the screen space, there is very little room for scaling before it causes clipping issues.

I think it would definitely be a good idea for Larian to address this. Not sure if it's practical to do it with DOS2 at this late stage but for future games, definitely. The first time I heard of XML being used for an in-game interface (17 years ago in Doom 3: dunno if it was the first, but the first I heard of) I thought it was overkill and a bit gimmicky, but it wasn't that long after that I saw just how much of an advantage it was when Oblivion's UI was given several comprehensive overhauls by modders to cater to all sorts of different tastes and needs. It'd be nice if DOS2 or at least its successors were similarly configurable.

That's unfortunate, but the UI itself is actually the least important aspect out of all of the things I mentioned. The size of the text is, according to my friend, just about large enough (it would only give less eye-strain), whereas the size of item icons are actually large enough. I can understand if the text boxes have been tailored to include all of the spoken text such that scaling them would cause other legibility problems.
Would it not be possible to, at least, allow just the map icons, like entrances and exits, alone to be increased in size, or is that still fully tied to the UI scaling?
And the other things I mentioned, are these not possible either without an excess of work (like permanent interactable highlighting, and walkable/reachable area highlighter?) Because the largest issue preventing him from progressing without literally combing over the map with the detached cursor is simply the fact that he's unable to see important interactable items like climbable vines, entrances/exits, important chests, loose keys and other key/items (although, the item name toggle fixes that with diligence).

Someone is looking in to the possibility of increasing the text size, but I'm not sure what the status is on that.
I'm not sure how much work it would be to allow scaling the map icons.

I can check with the programmers on the highlighting and icons, but I'm pretty sure something like that would not be feasible at this point.

Thanks for taking the time to read over my suggestions!
I understand that D:OS2-DE has been out for over a year now, where the time to give feedback for most major changes would have been before it's release, but I still think it's fantastic that you lot still read the feedback on the forums. Here's to hoping the implementation of some of these features isn't a major undertaking.

Unfortunately, the icons used on the map, etc, are part of the UI data files, so would be difficult to change/scale, and that wouldn't be possible with a mod (if switching to PC was an option). The highlighting is also not feasible.