User blog comment:Ḡwẵine Ḹٍٍkƨ Ĺiĸe Ͼềлȑềd/Where is everyone getting this Crystal Cave speculation from?/@comment-4650675-20121216201746

In many versions and movies, Merlin is trapped by Morgana/Nimueh/Freya (Morgana in this case, since the others are dead) in an oak tree, or a crystal cave :) so they are probably speculating that this will happen here as well