Hobbits hiding under the tree: I have the Escape off the Road plaque, pretty much covers that subject.
WitchKing/Wraiths vs Frodo/Hobbits: Nice idea, although I'm not sure about the scale of the entire piece.
Council of Elrond: Again, nice idea, not much action in the diorama but an memorable scene from the movie. And again, scale can be a problem (hobbits/"big folks").
Fellowship at the Gates of Moria: I already have the Gates AND the Watcher in the Water, so not quite looking forward to another huge dio.
Fellowship vs Cave Troll: Again, a nice piece but too much of a problem scale-wise. Either the Cave Troll has to be very big, or the Hobbits are very tiny.
Treebeard with Merry/Pippin: Lol, are you kidding me? Major scale issues!
Shelob with Sam: Hmm the Shelob statue wasn't really all that. Doubt that a dio like this would be much better.
Gandalf the White @ Minas Tirith: Nice choice, scalewise it would be best if this was a figure of him without the horse. Although I'm not too fond of GtW's likeness from SS so far.
Eowyn vs Morgul Lord: we have the statues that fit together just great, I don't see how a dio would add much more to that.
Sam carrying Frodo up to Mount Doom: Hmm... Frodo... Mt. Doom.. reminds me of the first dio. I was very much not impressed with that one. But maybe it could be redone in a good way hehe. It's definitely a memorable moment from the movie.