Alright, so I finished a short little comparison for Fereldan comparing it more to the time period of the middle ages. Just to let you know my perspective, I am not a fashion person, but I am a historian. Fashion is connected to history, as it is what people wore. With that said, here is Fereldan.
Fereldan
Fereldan is a based on anglo-saxon england if william the conquer was pushed out after conquering england. The Landsmeet for instance totally makes me think of the Witenagemot as an example. However in terms of actual fashion and what they dress like Fereldan seems to be more high and late middle ages for the most part then anglo-saxon, and in some cases more later periods.
Men's fashion
The above is a general idea of what men in Fereldan, at least the nobility tend to wear. Bryce is wearing a doublet of some sort. A doublet, while much more commonly worn in the latter periods of time first came into fashion in the 15th century. When one considers that Orlais is modeled after later years of France when it comes to fashion, then this makes more sense. You can also see the doublet, and some more later period fashion in the second concept art for the male.
Refering to the two concept arts for a moment, you can see in one the tabard for Fereldan. By the 15th century, the tabard became one of the more common ways for knights to identify whom they were. One's coat of arms helped show who you were.
For men though, the tunic, with an overgown(kirtle) was the standard dress for the men of wealth, ie nobles. The overgown or robe was actually rather common, so mages in terms of clothing would fit at home here.
The picture is of Jean de Vaudetar whom was the chamberlain of france. This helps illustrate the overgown. The king here is wearing an overgown, while Jean is knealing wearing a doublet. Ironically, it looks rather similar to the Skyhold outfit

Women's fashion
Now for women, Lets start with the concept arts pieces. The second concept art is much later in design then the middle ages, you can tell by the sleeves. Women in the middle ages rarely had such poofy sleeves. The first concept art is more fitting in with the various styles of the period. Looking at the noble ladies you can see that Eleanor is basically wearing the second concept art's dress, just less poofy.
The thing to keep in mind though is that compared to later centuries, the dresses of the middle ages were rather plain.The above images are of monarchs during the coronation. It also shows that there was some decorations, particularly how Philippa of Hainault(1st image) has her coat of arms embroided in her dress. All that said, compared to later centuries, the middle ages were rather plain; this works good in game as a great contrast between Fereldan and Orlais(or so I am hoping)
Another thing is that corsets did not exist in the middle ages for women or men(yes men at one time wore them too). Instead women as well as men used belts. In most of the images from the time period, you don't see them, due to it being worn underneath the main gown or robe. Looking at the images of Fereldan noble women though, one can see it being worn around the dress and most dresses in the game have some sort of belt or wrapper on the outside. This is not a universal rule though, as the image below showing the Hennin headdress proves; but for the most part the belt was underneath the dress.
Head-dresses
There is one piece of medieval fashion that we haven't seen really in the dragon age games, and I blame the engine for this. That is headdresses, hats and the like. While we seen helmets, we haven't seen much of the rather varied designs for headdresses. Often a hood or in the case of women some sort of veil style design was common. One of the more extravagant designs that arrived in the 1400s was the Hennin, see below for image, it was rather popular throughout france, burgandy and england. Though we haven't really got to see any headdresses for either men or women of fereldan besides a hood. Maybe that might change in Inquistion though.