I'm not going to weight in on if it's a good idea or not, but I will comment on my skepticisim in doing something like this.
First, you have to think about why PM is what it is. Is it because of the name? Doubtful. Is it because of the Everything engine? Possibly, on a lower level.
What I think has really made PM what it is, is the people here, and their passion for Perl. What is to be gained by a bunch of passionate Perl people starting JavaMonks? In my opinion, it will be Yet Another Messageboad. Will this JavaMonks site have noted authors of books on about Java? Will this site be frequented by people who have routinely contributed to the language?
If not, what's going to make it any different than whatever else is out there? I really think that something like that should be left up to those who are truly passionate about the language. If they have the preserverance to build a community like PM, then more power to them. However, the PM community trying to build a JavaMonks community would be hollow at best.
Anyway.. that's my opinion..