I'd like to see a game where you're pure human, elf, dwarf or uruk (take your pick at character creation) and you are thrust into war directly after the end of this game. Your character would be customizable and you could get armor sets to equip over the game (instead of this game and its static skins, maybe even break them into separate pieces of armor a la Oblivion), possibly even weapons, though I did like the rune system and the reforging aspect (and weapons usually have names and histories within the LotR universe).
At some point you would meet Talion and Celebrimbor, or maybe one of the Istari, and either get branded or be gifted power in some way and then go about raising an army while they bugger off and you don't see them for a while.
Taking your power you head off to gather an army. Obviously we've stepped into non-cannon land at this point, and you would work your way through the ranks in your respective armies, and possibly the Uruks (unless you're an Uruk and then you're pretty much limited to Uruks (exception incoming)). After you found yourself at the top you would lead your troops through a war with everyone vying for power. If you wanted to add a twist to it, you could make it where,
there could be someone working for the powers of darkness that was branding other captains in the good races.
The number of captains could even be increased by adding different races of man and elves (and possibly dwarfs, but a dwarf is a dwarf unless it's a DF dorf, then you've got a lot of psychopaths running around in tiny tunnels), making just the army creation phase into an easy two or three day venture. From there all you would need to do is localize the power struggle events per race, make the good races kill each other a lot less than the orcs (unless you decide to be an evil character), and then get a few more great voice actors and sprinkle generous portions of story wherever you want.
It's sort of out of the range of our current sized games, but I'd definitely be interested in playing it just with the Nemesis systems spanning multiple races.