It's safe to say that Bethesda had quite the showing at E3 2018, from showing off more of Rage 2, revealing Starfield, and confirming rumors about Fallout 76 being an online experience. The studio even announced The Elder Scrolls 6, though the company later stated it is very early in the development process. It has now been revealed why the studio announced the game even though it's only in pre-production.
In an interview with FZ.se, Pete Hines, Bethesda's VP of Marketing, went into a little bit of detail as to why The Elder Scrolls 6 was revealed with it being so early along. He stated one of the main reasons for it was to put some fans at ease, as the company thought some gamers would "freak out a little bit" when it was revealed that Fallout 76 was going to be entirely online. The reason for the worry, of course, is that the company is well known for putting out games that have a strong focus on single player. The announcement of the game was to let those fans know the company will still be releasing single player focused titles.
Hines also stated that the company wanted to reassure fans that it was still working on the next game in the franchise. A few years ago, Bethesda did say they would work on another Elder Scrolls game, but had two other titles it wanted to put out first. Those other two games are more than likely Fallout 76 and Starfield, both of which were also shown at E3. The studio wanted fans to know it hadn't forgot about The Elder Scrolls 6 and that it was indeed still coming.
The announcement for The Elder Scrolls 6 was very brief. All that was shown was a short trailer depicting a fly over of what is more than likely the game's setting, which had some mountains, plains and even what looked to be a castle in the background. No other information, including plot or setting have been revealed as of yet. There are some rumors going around about where in Tamriel the game may take place, though.
The Elder Scrolls 6 is in development for unspecified platforms.