There has to be a new engine, right? Every TES game comes with one.
Anyhow, I'd like it set during this "Great War" between the Empire and the Aldmeri Dominion that only gets mentioned in passing during Skyrim. I think you should start as a child like Fallout 3, and be able to pick a the races of both your parents and your place of birth anywhere in Tamriel. If you pick an Elf born in Skyrim, obviously you'll have a more difficult, risky life than if you were born in the south, but from there what you do is up to you. If you want to flee Skyrim and join the Dominion, that's up to you, or if you want to join the Nords in the Empire, that's also up to you, but ignoring and escaping the war entirely should be a real challenge. For example, if you've just entered a town you don't fit into, you'll be treated with suspicion. Do one thing out of order, you risk being arrested as a spy, then questioned, or deported back to where your captors assume you're from. Maybe they'll try to trade you for one of their own captured spies, or you could try an escape during transportation, although then you'll be hunted. Escaping and crossing borders shouldn't be easy, either.
The war should actually feel like a war. If you join an army and become a leader of troops, death should not be the only failure state. The Skyrim Civil War from TES5 just feels like 5 or six random skermishes that you can't lose, where the only way to win is to kill everyone. Nobody ever surrenders, even when their forts (which, by the way, you shouldn't just be able to walk in to) are surrounded, their outnumbered, and they've just watched one dude take out 20 of their troops. You should be able to give orders to attack, retreat, take prisoners, ambush, or just be a footsoldier who can choose whether or not to follow these orders. Also, a war shouldn't be centered around one person. In TES5, it's like there is no war until you decide it's happening. Just makes it feel tiny and unimportant.
Also, I'd like to see the Fame level back, but make it much more important than recognition. In a world of infinite opinions, any notoriety can be positive and negative at the same time. If you're well known in one place, (depending on the place) some would praise and some would jeer. Obviously if you're a war hero for one side, some places would cheer you, and others would throw things, run and hide from you, or possibly attack you on sight if you happened to have killed someones relative or something. A more notorious person would be targeted by more groups, also, for example a top-class killer could be abducted by the Dark Brotherhood, a master spy could be approached by the Thieves Guild, or a skilled Mage could be recruited by some Mages guild or College.
I'd also like it if you could create your own secret or public guild of self recruit-able, like-minded people with or without your own HQ if you have an interest in building up your independent influence to a point where you could stay out of the war, influence it in your own way, shift power among existing parties, spread philosophy, or just make money.
There's other stuff I'd like to see but I've just realised how much I've typed.