I recently came across this idea about the true nature of Tolkien's enigmatic Tom Bombadil on G+ the other day. Apologies for whoever posted it there, I couldn't find it again in a (lazy and quick) search of my G+ feed. Go read the link, it's not long. Then come back.
Did you read it? No? Need a tl/dr? The author claims Bombadil must be some sort of evil spirit who controls the Old Forest and Barrow Mounds, and only appeared as a cheerful jolly fellow to keep the hobbits from just running away.
When I shared the link with my D&D buddies, Dean posted this much better thought out and possibly correct theory of Bombadil. This one's a LONG read, in fact I'm still not 100% through it yet. If you've got time, though, and are interested in this sort of thing, I recommend it. tl/dr? Bombadil is an incarnation of the Song of the Ainur (and Ungoliant is the incarnation of Melkor's Discord).
Regardless, the first link got me to pondering running a game of D&D in Middle Earth. Not MERP (don't have it, have never played it) but good old D&D. I remember years ago James Mishler had a blog about his BX game set in Middle Earth. This would be (if I ever get around to it, maybe after the Chanbara play testing if this idea is still on my mind) a more-or-less standard D&D game, just using the maps and NPCs and trappings of Tolkien's work.
So an alternate universe Middle Earth, in other words. I think my guiding concept would be that either Morgoth was cast out but never imprisoned/chained, or else escapes. Or maybe the war against him ends in a draw, and he's still deep in his fortress, breeding monsters and plotting? Due to his influence, many other evil spirits enter Middle Earth, creating all kinds of monsters (as you'd expect in D&D) and the Valar send more than just five Wizards to combat them. In the past, I'd thought of using the Second Age (the Silmarillion stuff) as a more "legendary, heroic" sort of Middle Earth for D&D. Now, I'm thinking the good old War of the Ring time frame might be fine. It's more familiar to me and any potential players, although they'd have to be warned that this is not just a railroad Dragonlance style "play out what happened in the book" thing. Maybe I'd start the campaign in the time-frame of The Hobbit? Still considering that.
Would I run it with BX/BECMI slightly modified? That's tempting, and most likely the simplest way to do it. But I'd also consider using 5E. The ability to modify the subraces and backgrounds to fit Middle Earth, and with certain races and classes excluded or limited, it could work. It would be a lot more work for me to prepare that, though.