What do I mean by this? Well every Elder Scrolls game has it's own identity, feeling, and in a way, it's own story type. Morrowind was set in a very alien game world that did a good job of making gamers fall in love with it. Oblivion was a traditional good vs evil medieval fantasy. Skyrim was an epic heroes journey derived from Viking lore. So what should 6 be like? Well let's look at the prime canidates for ES6 and look at possibilities.
Hammerfell: A desert land with people dressed in Arabian/Middle Eastern style, a game set in Hammerfell could be seen as one of two things, maybe even both. Perhaps some themes related to the Crusades could be interesting as Imperial, Nordic and Breton culture could have a sizable presence in relation to the Redguard culture. And the crusades were more then just battles, they were also interactions between the West and East, and Christianity and Islam. This could lead to great culture based quests. On another hand, with Arabian like culture, we could have a main story that seems inspired from stories from 1001 Nights. With genies, monsters found from arabian mythology, sword weilding sailors, sorcerers who might be working in the system of government, and caves that might be harder to enter because you may need a password. Maybe the theives guild could be modled after the 40 theives.
Valenwood and Elsweyr: This is going to sound really weird, and if you have your own ideas for Valenwood and Elsweyr by all means speak your mind, but I've imagined a game set in Valenwood and Elsweyr would feel like a fairytale. You've got enchanted forests, cat people, forest spirits, many creatures that seem to come from your dreams, maybe even have at least one character in the main character be a prince or princess, and a group of evil magic users in the form of the Thalmor are ruling it all. Now of course it wouldn't be Disney like, this is still Elder Scrolls. But a game set in Valenwood and Elsweyr could work as a game where you are brought into a world of imagination and wonder. In order to make the game stay in line with Elder Scrolls lore however, Bethesda might want to get ideas from darker versions of fairy tales, or the rare number of fairy tales that are deliberatly written for adults or are parodies like Stardust or The Princess Bride.