In the context of a discussion about Nintendo, the PSP can't be called successful, though.
And the battery power issues have relatively gotten more acute since then, as have the performance issues. It's less viable now than it was then, and it's debatable whether it was a good idea then.
Err, the PSP would disagree with you. So would a whole generation of portable CD players.
I agree that SD is a better choice, or even the current gen of DS carts, but optical is not necessarily a killer.