I finished Lego Lord of the Rings today. Quite disappointed by the game, especially it being so buggy. The Lego builds in it are amazing though, and I'm convinced someone out there has made them in real life - I just need to find them. With all the tree stuff I've gotten lately, I'm pretty sure I could get a head start on Treebeard, but it's hard to figure out exactly how he's built. For the balrog, it would need a ton of special wing parts and printed curved bricks. The fel beast is probably a modified dragon body.
I can't really see Lego making mumakils, they would have to be almost AT-AT sized and entirely single-purpose, posable molds. But I'm almost convinced that we'll see some more of this realized, along with more characters.
* Eowyn vs Witch-King - this is a given, you'd get two new characters, the fel beast, probably a Merry in new gear and some random battlefield debris. Eowyn might not be important enough on her own, but this is a very epic scene.
* Gandalf vs the balrog - maybe a little less likely, considering the balrog would need to be rather huge. But it would certainly be a big seller, from what I've seen all balrog merchandise sells out. If the bridge is too big or hard to do right, they could have the mountaintop scene instead.
* Treebeard would be quite appropriate, after all the time they've spent improving their tree builds, and he's got a practical model already. He could come with Pippin and an orc to trample (with Merry already used in another set).
* Faramir - he seems obvious to put in a smaller $15 set with some random trees and another ranger, Madril or a haradrim soldier.
* Arwen (ranger) chase scene - a good way to add one or two more Ringwraiths, problem is that it would need yet another Frodo. Then again it's hard to find Frodo sets that don't include more random cliffs.
* depending on if the big character sets steal the high pricepoints, they may want to do another Helm's Deep type set with Minas Tirith and have army builder sets with orcs and catapults. This could add Gothmog and another Gandalf the White.