It most definitely would have an effect on the display. OLED displays have their advantages and disadvantages, just as IPS LCD displays do. Personally, IPS LCD displays is superior to OLED. OLED displays are nearly unusable in direct sunlight, while IPS LCD displays are relatively easy to use and can get might brighter. OLED's also seem to always have blown-out colors, but they definitely beat out IPS LCD displays in terms of black levels, although that seems to be changing. IPS LCD displays are only going to get even better once Apple moves to IGZO displays, which should bring major battery life boosts and possibly higher resolution displays that use far less power than current displays do.
Honestly, I don't think Apple will ever switch to OLED displays for their iDevices and future iWatch (because of crappy daytime visibility), and iOS 7 just proves that theory even more. The reason? iOS 7 is so white. OLED displays use the most power when the pixels are lit up white. That would be a huge battery drain on iOS 7 which has tons of white space in nearly every app. Don't bet on Apple moving to OLED anytime soon.