Is there enough in appendix to do 3 movies?
Well, yes and no. Take it very literal, and it's only a few pages compared to the books. But the amount of story in there, can lead to long dialogue and visuals. So you could certainly find enough material to make a third movie.
And I'll admit, it would be cool to see some of it on the big screen. The story of Aragorn past, and the story of Aragorn and Arwin can make for a very entertaining film I suppose.
But I'm kinda Middle Earthed out here. We wanted to do a marathon with a few people a few days ago, all three Extended Editions. After The Two Towers, we were all kinda done really. And yes, the movies are still great, they haven't aged at all. But still, in total we're going to have a lot of Middle Earth after the two Hobbit movies. I'd like to see Peter Jackson do something else for a change.
He's a very visual-minded director, and likes to tell stories and convey emotions with beautifull images. Sometimes that work, sometimes it doesn't. Look at George Lucas and Star Wars (mostly the prequels). Some thing, George tells stories through pretty images. Thing is, his stories are very basic really, so pretty images can only take you so far. With the right story (in this case LOTR) PJ did some great work. The charge of the Rohirrim in ROTK still get's me every time.
So I'd love to see something else by PJ, perhaps something completely by his own hands, or perhaps another remake, this time with a studio behind him that knows how to reel him in every now and then when it comes to how long the movie's going to be.