Since he already took on the trilogy, I'm sure PJ will somehow find a way to be involved in The Hobbit, whether it is as director, producer, etc.
Though if that does happen, pre-production probably wouldn't happen for another 2-3 years due to other projects he is involved in. Knowing how long it took to simply complete the first installment of LotR, any sort of The Hobbit movie most likely wouldn't be released until sometime after 2012.
Of course, that's just my guess....
