It seems Sony has in mind re-releasing physical copies of PSP titles on the new NGP media card game format. Sony has been releasing most PSP titles in digital format alongside (or shortly after) the physical retail copy hits brick and mortar stores, so it isn't a stretch to see them wanting to still have that library of digital downloads accessible for NGP owners.
However, something that wasn't particularly expected came out in an interview Sony did with Japanese site Gigazine - Sony told them that it has plans to re-release PSP games on the new media card format that the NGP uses. We don't really know what this entails, but one thing is sure, gamers aren't going to be happy if they are going to have to re-purchase their entire UMD library again for the NGP.
Sony is currently looking into different possibilities so that you don't have to repurchase your library, but remember how far that went when the PSP Go was launched? People thought Sony would be kind enough to offer digital copies of your UMDs free of charge, but that didn't go over so hot, eh? Still, something to keep in mind.