When I look the size of the Colovian Estate map, I think it's a chapter - No a simple map/quest DLC. The map size is equals those of Vvardenfell and Summerset.
However, Vvardenfell and Summerset have lots of cities (UESP considers that Vvardenfell have three major cities and one major city for Summerset)... Colovian Estates have two major cities : county of Sutch and county of Skingrad.
Another detail intrigues me : the count Calantius of Skingrad. He has the profile of an antagonistic leader. Except Fortunata in Dark Brotherhood, we find this profile of city leader in ESO Chapter.
The count Calantius gave his agreement for take the north of Reaper March in 582 of second Era. In general, the cities leaders we meet are loyal to their overlord and don't have pretensions beyond their territory (DLC map/quest and Vanilla game).
For Calantius, this is not his first attempt : 20 years before events of ESO, the West Weald invade the north of Elsweyr. This count is opportunist : he invades troubled territories (knahatain plague or missing resistance with principal force in center of Cyrodiil).
And considering the demonization of the Empire (currently messy), it does not help our dear count...
Given the charges against him, I doubt he was murdered by general Lavinia or Javad Tharn to justify that he is not behind the invasion. We do not even know if he knew about the daedric plot and Neither what he thinks.
Colovian states can be rich in terms of intrigues... Around Calantius or the Legion of the West Weald : between loyalists and conspiracy while they must ensure border security.
Personally, I hope the Legion will be there with the new profile in commandment. I do not think that the county guard is effective on the Colovian Estates borders.
We know that most of the soldiers sent to Arenthia are mere locals of Colovia... They deserted when they learned the daedric conspiracy. I wonder what the real soldiers in the profession do... Especially those who stayed in Colovia
The elite cohort came from Vlastarus... A village found itself in the middle of the front of the alliances war. The fort Vlastarus in west of village is in ruins (747 years later, it's a lair of vampires).
Actually, the Istirus outpost is decided between three camps.. (recent update). No info on the fort Istirus actually : The Legion is probably strengthening there to avoid overflowing.
[Sorry for my english, I tried to be as understandable as possible].