Before we explore this new, buffet-style rumored rights acquisition, let's consider what Amazon Studios has to work with in the first place. In an interview with Vanity Fair in the leadup to the premiere of Season 1, JD Payne explained, point blank, "We have the rights solely to The Fellowship of the Ring, The Two Towers, The Return of the King, the appendices, and The Hobbit," adding, "And that is it. We do not have the rights to The Silmarillion, Unfinished Tales, The History of Middle-earth, or any of those other books."
In that same interview, Patrick McKay pointed out that they have a lot of leeway to fill in the gaps in the lore as long as they're not egregiously contradicting the source material. Payne referred to it as connecting stars in the sky. While flexibility in storytelling is helpful though, if you don't have access to a piece of information in the first place, it's hard to connect dots and fill in gaps. That's where the new leak, if true, would be a game-changer. Fellowship of Fans claims, "For Rhun Amazon got special permission and access to two texts outside of the Appendices- one being from the Unfinished Tales around the Istari and consequently access to use all 5 wizards if needed. The other text they got access to is where Tolkien mentioned some of the Istari being around in the Second Age and travelling East."
As insignificant as getting access to a pair of minor text sounds, the ability to work with the Tolkien Estate to obtain rights for further specific pieces of information surrounding Tolkien's lore could be revolutionary.