Its kind of silly that not only would you advertise that you are working on a GPU miner for primecoin, but also that people would donate for one to be made. This will defeat the whole concept of Primecoin, and the value will plummet
Well there is the argument why not the OP just keep it to himself eh?
Think about that for a second, does it exist already?
We don't know and can only speculate.
I know if I had a GPU miner for XPM I would not share it. Why should I? At least not initially.
But then again that is the beauty of the free-market. You develop well you get rewarded for it.