Even if the the next iPhone fits in the cradle, that doesn't mean it will work unfortunately. There is a thread where someone modified a cradle to fit a new version but iDrive detected it wasn't compatible and rejected it.
It's taken almost a year for BMW to release the media adapter for the iPhone 4. Expect the same delay for the next iPhone. With this in mind, I recently got a 12 month contract for an iPhone 4 (rather than wait for 5)
F25 xDrive20d SE __ professional multimedia package | dynamic package | climate package | 309s | xline | xenons | electric seats | folding mirrors | business speakers