I read that it would cost about 10-12 million dollars to convert it. After the huge success with Avatar that would be money wisely spent. I hope Ridley pulls it through.
With that price it would cost Lucas about 60-80 million...?
I really don't think that too many people would pay to see the prequels again, 3D or not. And the old movies was shown theatrical just 12 years ago. So I understand why he'd held it back.
But than again, he's all for the new technology so I guess it's just a matter of time.