That's the thing about TES: in real life, there would have been many expeditions of merchants, soldiers, and missionaries to Akavir. In the world of the Elder Scrolls, the continent of Tamriel is content to leave Akavir as a mysterious, unapproachable land.
That's fiction for you, it doesn't have to follow any sort of realistic logic as long as it achieves whatever goal it aims to achieve.
Fan fiction, but that's what one would look like. I don't think the Tsaesci would build other cities. The kamal don't live in cities, they just ctawl out of hell in the summer to kill and [censored]. The Tang Mo live subsurviently to the Ka po tun among Tosh'raka's "Scales of Heaven." Which is their own Aldmeris.
If it's from fan material, than it should be completely ignored, since whatever fans say has absolutely no bearing on canon, unless in the event that the developers just say "Sure, why not?" and decide to throw a fan theory in there just because it's kind of a good idea, or some fan eventually manages to land himself in a position where he can control what happens in future Elder Scrolls games, and decides to put his favorite fan theory in the game (This kind of thing usually is limited to cases where a series runs long enough, of course, but I suppose it could happen.)
At best, any fan material is speculation based on existing hints that may or may not turn out to be inaccurate, at worst, it's something a fan just completely made up out of nothing, in general, fan fiction can be enjoyed as good stories based on someone else's material if it's actually good, but one must never make the mistake of assuming it has any bearing on the canon universe, the Elder Scrolls universe is not a collaborative work created by the fans, it's a fictional setting made by Bethesda.
But yes, I'd imagine that Akavir has its cities, after all, there are people living there, and if you have settled, civilized people, cities seem like the logical path of progression. Now what do the cities look like? Who knows, I'm leaning towards something along the lines of the stereotypical traditional Chinese or Japanese city, at least for Tseasci, with of course snake people replacing humans, because seeing Bethesda reduce Cyrodiil to Generic Fantasy Land in Oblivion has caused me to lose confidence in Bethesda's ability to continue to provide creative environment designs, and we already know that there's at least some Oriental influence in the snake-men. But as long as we don't see the real thing, we can't say for certain what it's like, so we can make up our own ideas, even though if we ever do see Akavir in any games, there's a good chance it won't be like what we imagine.
For the other races, though, I honestly don't know, I suspect that the Kamal wouldn't really have cities, since from what I understand of them they don't exactly sound like the city building sort, if they're even sapient at all, it isn't entirely obvious that they are. The other races, though, who can say?
The cities are mysterious because we don't know what's there, that dosn't mean the denizens are mysterious.
Well, I'd say the denezins are kind of mysterious too, since there's also a lot we don't know about them, and what we do comes from sources that could be quite outdated in the context of the Elder Scrolls universe, and could potentially be inaccurate, seeing as books in the Elder Scrolls aren't always right, much like in real life in that respect.