Let's just say Nintendo and Sony's next handhelds come out at roughly the same time. At that point, I'd expect PSP sales to nosedive and DS sales to remain pretty high a few years into the new cycle. Only winning consoles have ever had the momentum to last into new cycles.
So PSP will continue to gain marketshare on DS for the immediate future, but eventually DS will make marketshare back. Whether it makes it above 70% is anyone's guess.
Of course, if the next Nintendo handheld comes out a year or more before the next Sony one, DS might never start gaining marketshare again. But does anyone really see that happening? Outside of the Japan turnaround, PSP is running on steam. Every several months some publisher slams the system. I'm not saying they'll do it in the next 18 months, but Sony should be ready to reboot PSP before Nintendo moves on from DS.
"[Our former customers] are unable to find software which they WANT to play."
"The way to solve this problem lies in how to communicate what kind of games [they CAN play]."
Satoru Iwata, Nintendo President. Only slightly paraphrased.
