The new series will explore Middle-earth in a time period before the events of The Lord of the Rings — but given that Galsor says that it will concern “previously unexplored stories,” we might not be looking at another adaptation of The Hobbit either. That leaves two options: Amazon could plumb the depths of the appendices of The Return of the King, potentially detailing the early romance of Aragorn and Arwen, the creation of the Rings of Power and the history of the line of kings from which Aragorn is descended.
Or, in what would be more of a revelation for Tolkien fans — and provided that Amazon had also purchased the television rights to the author’s The Silmarillion — the series might have the entire history of Middle-earth from its creation to play with. Amazon’s press release does note that the deal with the Tolkien estate “includes a potential additional spin-off series.”Regarding The Silmarillion: I was under the impression that Christopher Tolkien was 100% opposed to allowing anything like this to be done with it. (He loathed the LotR + Hobbit movies.) But I would be delighted if he has changed his mind!
Even if The Silmarillion isn’t covered, though, there is a goldmine of storylines in the LotR appendices. And since those storylines are quite sketchy, there would be more room for writers to be creative with them within the overall framework of Middle-earth.
As for Amazon hoping that this might be ‘their Game of Thrones’, I think that they should remain true to the distinctive character of Middle-earth. While the Akallabêth (the tale of the fall of Númenor) is kind of ‘GoT-ish’ (with it many nefarious actors and the Stark-sh House of Elendil), Middle-earth is much more black-and-white than the GoT world. That should be retained—if not emphasized—not downplayed. Viewers might be in the mood for such a change (especially given how GoT-ish the real world seems these days).