I'm going to go say my piece before Kotaku, Polygon and every other site is publishing articles about this because you know it's coming.
I find it odd people are surprised to see a black person in the trailer. Everyone seems to forget about South Gondor, a desert land that Gondor has lost grip on and borders on Near Harad.
Rhun and the Sea of Rhun is connected to the Celduin, a river that connects to Esgaroth, Dale and Erebor. One of Middle-Earth's wealthiest places and biggest trade routes. People of color exist in Middle-Earth and they're not from some far flung "far away land" unless you're a hobbit, in that case, everyone is (and even then, some hobbits travel to Bree from time to time and there are Breelanders of color).
An argument can be made that Lord of The Rings (and Tolkien's works in general) are heavily inspired by Norse Mythology (Beowulf) and thus the saga takes place in a primarily Norse and Celtic environment. Which, it kinda does, as Middle-Earth is to a lesser extent, the "Europe" of Arda (the entire world). And Harad and Rhun are on the borders of Middle-Earth (and also less fleshed out lore-wise than the other cultures and civilizations of M-E). There are countries like Rohan which clearly evoke vikings and Saxony.
I am not 100% sure but I believe there aren't any characters of color in any of Tolkien's works, Tolkien grew up in a Europe that was far less multi cultural than it is today, and perhaps also a little more sexist. There aren't many female characters in LOTR either. it's an older story now, a story written in another time (I'm not saying Tolkien was a racist or sexsist, but his world view and inspirations were clearly of their time). But the lore implications are there, people of color exist in ME. Yes, most of them were 'aligned with Sauron' but even then, Tolkien goes out of his way that they weren't the same as say, Orcs.
"You wonder what his name is, where he came from. And if he really was evil at heart. What lies or threats led him on this long march from home" - Sam (yes, it was Sam in the book)
Is it such a strange thought that some of them thought this? And questioned their reasons for going to war for a freaking Dark Lord in his volcanic ash land? Nah, they had motivations beyond just "fuck shit up" like Orcs and Uruks. These are books we're talking about, and so the visualization and imagination is up to the reader. Like I said, the lore implications are there, it's totally in line with the world so there is no reason to be upset about it other than....racism I guess? I can't think of any. The only thing I can't really justify lore-wise are Asian people, because as far as I know Asia doesn't exist or is so far away from the events of LOTR that they're just not around.
TLDR: everything about the lore indicates people of color were in Middle-Earth, perhaps less prominent, but they were there. So suck it.
A Tolkien nerd.