Will this improve, preferably before launch?
Right now, the UI is just not good. There is absolutely nothing good about the UI for PC right now. If you want to be a producer & trader, the UI does a terrible job of helping your business.
For one, selling actual products of the same quality and type appears to requires setting every item individually. Same goes for buying those items. Want to sell 100 armors for a specific price? You have to do the same action 100 times.
Then there is the problem of how much space is wasted for useless information. Searching for a specific items gives a long list, which is even longer due to the same items from the same seller for the same price showing up individually, and each item displays its icon which makes is row about 2-3 times larget than it has to be. If you want to know how many items there are for a specific price, you have to count them manually.
When you have the same item for the same price about 100 times, the space used in that list is about 200-300 times larger than it has to, as it uses 100 rows which are bigger than they have to be.
Next up, Filtering. It is serviceable, but could be easier to navigate. There are filter options which on their own are fairly useless, like Armor. You almost always have to specify the actual type of armor you are looking for. Also certain options should do not work without filtering, but they still populate the item list without filtering. The prime example for this is setting up a buy order. When you enter that section of the auction house it will immediatly populate a list of items without any filters applied. It literally is a list of all possible items (besides that you cannot set Quality there).
So how could this improve? Well a start would be to simply copy the functionality of Eve Online's market. The look should also be similar, but obviously with a medival spin.