Disclaimer: English is my second language.
Skyrim is just a great product in so many ways —it knows how to keep the player engaged with its great ambience, nice background storytelling and satisfactory gameplay. TES 6 should take from Skyrim by also improving what Skyrim lacked: a good faction system.
I think this is the evolution path this games should take. We saw a glimpse of this mechanic with New Vegas and a devolution of some sorts with Skyrim's Imperial vs Stormcloak beef. An improvement by which the player can make a faction gain terrain, freely shape shifting the games narrative on the go, is a great improvement to the former.
Think of it like this: you are exploring a dungeon and you could just open your tactical map and bring troops of the faction right where you're at. You could also command and rank the troops and they'll develop a personality if they accomplish something. The same way your enemies would do and develop their own ranks (let's circumvent the Nemesis trademark for a minute) and you would see their advancements and this would alter dialogue and missions.
It would also be cool to have a mechanic of administering rations. Like you could only rest in a tent your troops would set up for you and preferably be accompanied by the troops you have developed a deep bond with, like your A team. And you could strip of your bannered wears to enter into the enemy cities anonymously.
I know it seems to deviate a lot from the series, but carry on with me. This could be the next step this franchise needs to take.