I feel like Palantirs are such a lore friendly thing to add. Replicating the Palantir is diffciult in Minecraft. But the best way I think of how it could be replicated is to create a full or half sized map that is fully explored. The map would have 20 durability and each use would use it by 1. This would allow a player to quickly explore parts of the world. It isn't used how it is in the lore but I think it matches the point.
Since it is a powerful tool it would only spawn rarely in Arnor and Gondor Ruins.
I am not an aritst but If I were I would add a texture. But in my mind it should look like an eye of ender but with red's and oranges instead of the greens. The center eye would be surronded by almost pitch black shaded to look smooth with the eye. The Palantir would be placeable to act as a decoration if desired and would have a spherical shape like as best as minecraft can do, on the ground. In the movies we see the palantir placed on a pedestil I am suggesting something like that.
This isnt the most important thing; but I think it would be cool to add, and provide a useful tool for the insane world. Maping it would be much easier with such a tool.
Edit: After going over some rules I decided to add some more description.