There are many different time periods in the history of Tamriel. Since we have been playing mostly during the late Third Era, we obviously know the most about that. Likewise, we know quite a bit about the later 4th era (well, for all we know it could be early because the 4th Era will last 10,000 more years, but there's no lore on the 4th era after 4E200) from Skyrim, and doubtlessly there is going to be a bunch of lore on the early parts of the Interregnum in Elder Scrolls Online. But there are plenty of periods we don't know as much about. I have divided the times in Tamriel without games into 13 arbitrary ages. Of these ages, what would you like to see more lore about?

Late Merethic.

The Velothi exodus, mostly dealing with the great houses and chimer tribes and the history of the founding families.

Dwemer disappearance, Middle First Era