Things with a good UI tend to come from the big, soulless capitalist monsters - because they hire people to specialize in it.
A "good UI" (and UX) is also very much subjective and depends on what you're used to.
Mmh, I agree that there is a level of subjectiveness to it, as interfaces are learned, but:
a) standards exist, formalized or not, and they serve us well. If most people are used to processes working a particular way, symbols have a particular meaning, we should by default conform to that unless there is a good reason not to. Otherwise, the argument is basically "preferred language is subjective, so my forum posts will be in swahili instead of english" - sure, but that would make it a pain for almost everyone else. Using english is not a perfect compromise, but it works better than all the alternatives.
b) independent of subjective design tastes, there are loads of low-hanging fruits - for example unsearchable dwarf lists when assigning tombs or military squad membership. I don't know by what measure these lists are sorted, but searching through 120+ dorfs to find the one guy I want to add to a squad is just a pain.
For instance, since I don't have a smart phone (or ever used one), most modern interfaces which have been made with a smart phone user in mind are utterly horrendous for me. Give me a UI from decades back and I'm much more comfortable with it. That's one reason why I've never really had issues with the old DF interface (I mean, I loved even 'umkh'!) and why I am reluctant to play the Premium release (also, lack of 100% keyboard control keeps me away).
(...And no, I'm not expecting that the DF UI should be made to suit my old fashioned tastes. I know I'm pretty much in the minority and that's just what I'll have to live with.)
I totally feel the smart phone UI thing! I managed to avoid one until around two and a half years ago and the swiping still vaguely annoys me. And I also agree on keyboard controls, I still occasionally hit old control combos when I want to do something in the steam version. Perhaps the soulless corporate dig was a bit misleading, the UX improvements I would like to see in DF are more along the lines of consistent filter/search/sort functions, a better labour interface - this being a prime example of a sorta half-assed improvement, before the steam version, fortress mode was (imo) unplayable without dwarf therapist for labor assignment, now there is a barebones interface for it that needs a ton of categories added manually (unless you want lots of shitty weapons while the legendary weaponsmith is picking flowers somewhere). Its an improvement, but still very annoying to add a ton of labor categories by hand every fort. And that's what I mean - making a good UI for dwarf fortress is a significant chunk of development time, increasing with every new feature and system. I don't think it is productive to have Toady spend time on it, I'd rather have fancy new things added to the game - i.e. the old "Dwarf Fortress plus a modding community that adds vital UX stuff like dwarf therapist" system. But, with the big steam bucks rolling in, and from a business (and, you know, general accessibility) perspective the sensible idea of making it easier to get into and play the game, hiring somebody who solely focuses on User Experience could be doable and would mean the best of both worlds.