In all honesty, I feel that the DS will easily reach 112 million, although I have my doubts that the PSP will achieve 67 million in the same timeframe.
But you never know what will happen. The PSP has just recently had it first decent price reduction in both the US and in the UK, although it is still more than the DS. I can see no reason why the price cannot come down to around half the current price over the next 3-4 years as well. The games need to continue to be released and the quality and uniqueness of the games need to be upped as well. Hopefully Sony will dedicate more time to the PSP, especially once all the development for the PS2 stops.
Longevity wise, I can so no reason, unless the games dry up, that the PSP cannot have a 7,8,9 or even 10 year lifespan with new games coming out. The postive thing about the PSP, is it's ability to develop addons and new firmwares that expand with time and allow for more functionality. Also, the actual power of the system is enough to hold off a new Nintendo handheld for a while seeing as it is vastly more powerful than the DS. Although as you know, power isn't everything.
What these figures demonstrate is the acknowledgement that handheld gaming is bringing new gamers in all the time. And I reckon it will continue to grow at a faster rate than the home console market. That is until the cost comes down.
Prediction (June 12th 2017)
Permanent pricedrop for both PS4 Slim and PS4 Pro in October.
PS4 Slim $249 (October 2017)
PS4 Pro $349 (October 2017)