Hideo Kojima's said he may do another iPod/iPhone title after the "success" of Metal Gear Solid Touch.
Hold onto that hat, though: this time it could well be something "crazy".
From this G4 report of the developer's visit to San Francisco's Apple Store following his GDC keynote:
Finally, Kojima is open to doing another iPhone/iPod Touch game, but it might be something completely "crazy." One of Mr. Kojima's favorite apps is the lightsaber app. He would also like to do something that uses even more of the unique capabilities of the iPhone platform. For example, say you listen to a lot of Coldplay (his example, not mine)... if you then listen to Coldplay while controlling Snake, he might fight better. Interesting stuff.
Sounds mental. More through there.