TWRoO on 26 October 2008
There hasn't even been a handheld to outsell even old generation Nintendo handhelds yet.
If you split up GameBoy and GameBoy Colour then it's about half and half I think, which means the PSP may surpass one of them by the end of it's life.
As for your question, I'm sure it will happen sometime, but I can't forsee a situation where it will in the immediate (10 years) future.... and in ten years time I imagine I could add a further 10 years of foresight to say it probably won't happen.
