So i've actually been thinking about doing this for a long time I just could never emember enough of my ideas to write this so I'm going to attempt to remember them all. Feel free to comment and add more.
1. The Tsaesci- They are (according to the wiki) vampiric snake-men. Now there is a lot of dispute of what they look like so i'm going to stress one word. VAMPIRIC. Take vampirism in skyrim for example. Feeding on blood lessens your affliction same rule applies for the Tsaesci. This probably means they eat something to be disguised as them. Which would explain why there is so much confusion as to wether they are what their picture looks like or they are human. This would make sense cause they always want to eat/assimilate something. Like the dragons in Akavir.
2. Unnamed Daedra- For those of you who read Lord of Souls i'm hoping you'll remember what I'm talking about. When Collin went to find Hirem's Secretary's journal he encountered a ghost like daedra. According to an in game book whose name i think is Doors of Oblivion, the realm of Hermaus Mora is filled with ghosts. Daedra realm filled with ghosts + Ghostlike daedra = Daedric servant of Hermaus Mora.
3. Traitorous Rebel- During the quest diplomatic immunity you find the Thalmor dossier of Ulfric Stormcloak. I believe it says something about severing contact with Ulfric. So my fellow Stormcloaks it looks like Ulfric may be a Thalmor traitor.
4. Hybrid- For those of you who read the Book Beggar Prince in Skyrim/Oblivion you know of the three blessings of Namira. One of which allows the prince to have any disease so long as it affects his form somehow. So he could effectively be a vampire and a werewolf. This means we must all go worship Namira (JK).
5. No Firearms- Fire arms have been a long disputed subject with the Elderscrolls. Many people believe that there should be firearms on Tamriel because so much ttime has passed ,but there is a reason they haven't been invented. Scholars and Mages are becoming less intelligent. If you look at the magic in any Elderscrolls game, and compare it to Skyrim you realize that Skyrim's magic is less advanced. So intelligence is effectively going down so every time some ones "discovers" gunpowder they end up blowing themselves up.
Now i'm tired, and i can't remember anymore so i'm feel free to add your own. Peace.