The White-Gold Concordat was imposed on the Empire by the state. This treaty made the worship of Talos illegal and made the Empire a servile nation to the Dominion. The Empire was not a vassal on one hand and on the other it did not have the power to do what it wished for either.
This is the political scenario of Skyrim, which was essentially a rebellious land under the rule of the Empire while also overseen by the High Elf police or Inquisition- The Thalmor.
Irrespective of whether Skyrim ends up as an independent kingdom or remains a submissive nation to the Dominion, the clutches of The White-Gold Concordat still remain strong on it and the Empire grows weaker by the day.
This aspect should be focused by the developers in the next installment of Elder Scroll games. Also, the defeat of Aldmeri Dominion at the hands of the Empire is another aspect which has not been narrated in details in Skyrim and fans would definitely want to see more exploration regarding the same aspect in Elder Scrolls 6.
However, to make this happen the developers do not need to necessarily set the game in Summerset Isles. Fans would love to get a chance to bring down the Thalmor and the Dominion, given the fact that the developers continue the same timeline as that of Skyrim in Elder Scrolls 6.
It was stated in another report that the Dragons awakened by the Alduin in Skyrim will make its way back in Elder Scrolls 6.
Stay tuned for more update on Elder Scrolls 6.