Most previous reports had suggested that Amazon's project would be set between The Hobbit and The Lord of the Rings and would focus on the adventures of a young Aragorn. However, Amazon's maps suggest that the story could be set considerably earlier.
The first clue was on the second map released (after the first, blank one), which named the major regions of Middle-earth but left the Shire, Gondor, Arnor and Rohan off the map. Most tellingly, the map features "Calenardhon," the ancient name for the lands south and east of Fangorn that later became the kingdom of Rohan. The presence of "Calenardhon" immediately suggests a setting prior to the founding of Rohan in the year 2509 of the Third Age (518 years before the events of The Lord of the Rings proper begin). Although Calenardhon was the name of the north-westernmost province of Gondor before it was ceded to Rohan, the name was also a regional one; it's earliest chronological use in the canon is in the story "Aldarion and Erendis" in Unfinished Tales, which it is used as a regional name as early as the 8th century of the Second Age, long before the founding of Gondor.
The third map adds more names and further suggests a time period. In particular, the addition of the name Laurelindórenan is very interesting. This was the Sindarin name given to the elven kingdom later known as Lothlórien. The mode Laurelindórenan seems to have been the standard name used until around the time of the War of Sauron and the Elves, following the forging of the Rings of Power, when Galadriel and Celeborn took up leadership in Laurelindórenan and the name of the realm was changed, as a result of Galadriel's magical ring enhancing the natural beauty of the kingdom.
A mural depicting Ost-in-Edhil, capital city of Eregion, by artist Alan Lee. This artwork was created for Peter Jackson's Lord of the Rings movie trilogy and appears on a wall in Rivendell.
The logical conclusion, then, is that the "Young Aragorn" story has been dropped and the story will instead focus on one of the most interesting periods in the history of Middle-earth: the forging of the Rings of Power themselves.
There are other possibilities, such as "Young Aragorn" still being the setting and the story will revolve around this map and backstory in some fashion. There's also the delicious possibility that the series will be an anthology one, with different settings and focuses each season, moving back and forth through Middle-earth's history.
Most intriguingly from all of this is one of rights. The Tolkien Estate is working closely with Amazon but, until now, had not confirmed or indicated if it had licensed the rights to any other Tolkien material, as Amazon's deal with New Line/Warner Brothers (itself licensed from Tolkien Enterprises twenty-four years ago) covers only The Lord of the Rings alone. Not even The Hobbit is included, as those rights are tied up with MGM and, after the fiasco of the Hobbit movie trilogy, it was decided not to involve MGM in this new project. However, the detailed account of the War of Sauron and the Elves and names Andrast and Ras Morthil are given only in Unfinished Tales, not The Lord of the Rings. To use those names, at all, Amazon must have reached a new licensing deal with the Tolkien Estate on pain of lawsuits. The previous Middle-earth movies had to go to some lengths not to use any material from Unfinished Tales or The Silmarillion, so the use of such names here is highly telling.
The truth of the matter should become clearer as Amazon continues to reveal more information.