My understanding is that PJ didn't start with "The Hobbit" because New Lines did not own the rights to it, and another company did. That at the present moment New Lines is trying to secure the rights to "The Hobbit". PJ has said that he would be willing to film "The Hobbit", but after a break (he's been working on these three films after it's all done for 7-8 years).
Let's just cross our fingers that New Lines can come up with the millions to secure the right to "The Hobbit" and PJ gets a good rest before production.