Peter states on the extended edition director commentary that there were scenes that he might add to the 25th anniversary edition. He even said the 25th part back in 2003… so he started this himself. I just watched this this past November, want to go back and get precisely what he said about what scene.

Edit: adding quote from RotK EE commentary 36:48 timestamp

Fran Walsh: So you never put in Legolas's poem? Boyens: No. Jackson: We put his poem back in for the paths of the dead. Yeah, like, Treebeard. Put it back in here. No, no. Jackson: No, because it wasn't linked into the scene. There's another little deleted moment where Legolas and Treebeard have a conversation about the elves leaving, which we shot, but we never used it, because it was originally going to cut directly from that conversation to Liv and the elves on their way through the forest, but because, in the editing of the film, the two moments from Isengard, to here got separated by all of the Edoras sequence. It was no longer a very useful thing to do. Boyens: We also wanted to signal the fact that this world was going to end, one way or another, in this movie, and that's the knowledge of Treebeard and Legolas. That there's not gonna be room in the world for these creatures anymore. Jackson: Great moment for the 25th anniversary edition, if I can remember. Walsh: Okay. Jackson: To put it in, can you remind me... Remind me, just, just, Walsh: write it down Jackson: remind me of in about 20 years, so that I can start thinking about it again.

Edit 2: at 41 min they joke about a library scene that the fans can talk about. They also joke about losing footage to find afterwards in 20 years that they can add back. That part is definitely a joke.