I don't get why people think an announcement is coming soon. Fallout 4 was finished up only about a year ago. Historically, Bethesda works on one series at a time. If that's still the case then they've only been developing the next Elder Scrolls for one year. Yes, a lot of early planning and artistic work might already have been done but not the real substance.
There is also the speculation that they might be switching game engines (ha) which would extend development time.
Of course, it's always possible that they changed their routine and hired more people to start work on Elder Scrolls early, or had their new studio work on it, but I would need some kind of confirmation before I trusted that assumption as plausible.
Finally, Bethesda doesn't like to make announcements early. Fallout 4 was announced just a few months before release.
