A man is known by his friends, the devil is known by his fiends
These will be limited to the smallest models, but whether we're talking a replacement for the Shuffle or the Nano is not clear yet.
While OLEDs may look gorgeous, with excellent viewing angles when viewed indoors, they fare much less well in bright sunlight, becoming about as useful as a piece of blank glass.
Of course, in an Apple, they'll be the coolest piece of glass in existence, but not so good for reading your MP3 track name. Still it's one up over the current Shuffle.
Small passive OLEDs are pretty good in terms of reaction times, performing fairly similarly to a TFT, so viewing small video podcasts should be no problem. There is also now becoming good availability (in small sizes, at least) of the even better-performing active AM-OLEDs which are built on similar glass to TFTs.
The other big problem, however, with them, is the short lifetime. In particular the different coloured LEDs fade at different rates, and can leave you in just a few thousand hours of viewing with a very odd-coloured display.
So it might match the discoloured white plastics if they make them from the same material as the new iBooks. µ