Anything story set in the Second Age is extremely vulnerable to forgone conclusions. But the Second Age is also full of holes to be filled in, since it read like a history book, and Amazon's show should take advantage of that.

As result, in my opinion, most of the main characters should be original characters, created just for the show, who's stories coincide and juxtapose with those of characters who are found in Tolkein's books. If you've read my posts before, you know what I mean. If you have not, I personally think that these characters should be called "The Forgotten Heroes", as history forgot they existed... until now.

But what should their story actually BE? My hunch is that it will be another quest, a group of heroes of the various races band together, and travel the Middle-Earth of the Second Age. But for what? For something that could help turn the tide of the conflicts against Sauron that are established in the Second Age? To take out an original Second Age servant of Sauron? Something else? Let your imagination run wild.