TORN is reporting this from a recent Del Toro interview at the Los Angeles film festival.
=====================================================
"We believe there is a second movie, if there isn’t, there will not be. If we find it, we will shoot it, but by God, if we do not find it, we will not shoot it. I am anxious to shoot the book, and I’m willing and able to dedicate myself to shooting the [second film].
In the four books that are in the domain of the copyright, there are appendices and ideas and things that can be traced without risk. But I have to be careful not to overstep. We believe there is a way to create this film and make it interesting, but it’s too early."
==================================================
Sounds like he will not just make any crap with the name Middle-earth attached just to make money for the studio. And that sounds good to me. In the same interview he expressed disdain for bankers and making money so maybe he has strong socio/economic/ political views which are coloring this statement.