This may be a bit unstructured, but:
I think the one major hurdle is that the game doesn't explain itself at all. I remember the first time I ever booted up the game I literally had no idea how to get anyone to do anything: you don't even realise that the dwarves are autonomous, and they don't really act like it until something pesters them. So you're looking at your guys waddle around a bit and then they die. And you've tried to get them to do something, but you can't select them and there's no explanation as to why. You've just got a big bar at the side that seems to be a series of buildings that you can't build because you don't have the resources and you seemingly can't get the resources.
I can't even remember if there's a standard loadout that you get if you don't start with a specific roles and equipment, and I can't remember if that's a thing you have to toggle on for each dwarf or there are some basics turned on by default. Then, assuming your dwarves have some jobs, there's no way you're going to notice the jobs toggle screen, the fact that you need to designate stockpiles to get your dwarves to bring the things back so they can use them, the nobility that is necessary to assign new jobs, the fact that you need a book keeper to know how much of a thing you have. Just that basic level set up chain is never outlined.
I'm not sure it's worth doing a full on tutorial for this game as it changes all the time. But a basic little sub-screen that runs you through the concepts of the game and some scenarios so you at least know roughly what the mindset of the game is. Get your dwarves to dig, setting up stockpiles and getting them to gather resources, how the jobs system works, etc. You can pretty much just bounce from one thing to the next as long as you know how the game thinks, but you need something to be able to intuit from first. I think the base level of unintuitiveness is more a sidestep from the expected frame of mind, rather than a complete alien concept. But people need to have a starting ground so they know what they should roughly be looking for, if you see what I mean.
Other concerns: Just some basic quality of life stuff: consistent keybinds, so moving through a series of menus doesn't inexplicably require three different sets of controls - that kind of thing.
For the entrenched players:
Some way of exporting and importing job orders. The automation was probably one of my absolute favourite things you guys have added in a while. The sheer time it can take to set things up in Dwarf Fortress will often just block my desire to actually start a new fort. I spend a little while looking for a spot, I do the setup, I then have to designate a half a dozen things and set up some stockpiles, farms etc, and then add ten plus rules for basic food, brewing furniture, etc. I think just being able to import a series of job rules would speed the launch a lot. I think most forts are going to start roughly the same per player, so you may as well skip the basic stuff and diverge from there, get to more of the guts of the game faster etc, than spending literally an hour or more before you're even able to unpause the game.
Position based rooms, and furniture designations. I know that there are mods for this, but it makes sense for it to be in the base game: Nobody wants to have to constantly assign new studies for their nobles every time one of them gets killed or goes crazy or whatever. Just let us designate X chair goes to the book keeper, or this room belongs to the hammerer, etc. Much in the way that basic unclaimed rooms work. That also just cuts down the tedium. If a player wants to reassign individuals to specific rooms they should be able to, but most of the time I'd assume we don't care that much. Book keeper dies? Next one is assigned and knows where their quarters are. Similarly, I don't want to replace every chair, table, and door individually because a troll didn't like it's beer. designate the tables, if one gets broken the game knows that a table should be in that square and another is chosen to replace it from the stockpiles. Cutting down the intrusive bits of tedious micromanagement could smooth the experience a lot more.