Apparently, the estate has pretty firm guidelines about when the show can take place, too:The Tolkien Estate will insist that the main shape of the Second Age is not altered. Sauron invades Eriador, is forced back by a Númenorean expedition, is returns to Númenor. There he corrupts the Númenoreans and seduces them to break the ban of the Valar. All this, the course of history, must remain the same. But you can add new characters and ask a lot of questions, like: What has Sauron done in the meantime? Where was he after Morgoth was defeated? Theoretically, Amazon can answer these questions by inventing the answers, since Tolkien did not describe it. But it must not contradict anything which Tolkien did say. That’s what Amazon has to watch out for. It must be canonical, it is impossible to change the boundaries which Tolkien has created, it is necessary to remain “tolkienian.”
Basically, that meant that if you've been waiting for a Tom Bombadil spinoff, uh, you're going to have to keep waiting.Along with these narrative details, the guy also shared some information about the show itself. According to Shippey, the first season of Lord of the Rings will be a whopping 20 episodes long—quite a few given the amount of money Amazon is throwing into this thing. The show is still in development, but it's supposed to go into production in 2020 and presumably hit Amazon at some point during the next couple years. At least it'll be here sooner than the third season of Fleabag.The First and Third Ages are ‘off-limits’, you can’t have the First Age. Events could be mentioned at the most if they explain the events of the Second Age. But if it is not described or mentioned in the Lord of the Rings or in the appendices, they probably cannot use it. So the question is to what extent they may hint at events that took place, for example, in the First Age, but still continue to affect the Second Age. There are several maps authorized by Tolkien, not just the ones we are familiar with, and some of those maps have places on them which are not in the other maps. But if Tolkien authorized them then that’s okay. So it’s a bit of a minefield. You have to tread very carefully but at the same time there is quite a lot of scope for interpretation and free invention.