If not Redfall, then what?
We're a long ways away from The Elder Scrolls VI, but the wait could potentially be a little longer. A Redfall trademark was filed by Zenimax in September of last year, but said trademark is currently being disputed by an author. This dispute could potentially push back the release of The Elder Scrolls VI depending on how it plays out unless a settlement is reached or the developers change the game's name.
What is Redfall exactly? In the context of The Elder Scrolls, no one knows. The Redguard come from Hammerfell and Redfall isn't one of the provinces of Cyrodil, so it seems like this is more a thematic name than anything else. If it's not the name of a place, it would certainly be breaking with tradition—Daggerfall, Morrowind, Oblivion, and Skyrim are all the names of places in the universe of The Elder Scrolls. It could, of course, be a brand-new location that we haven't yet seen.