We still have not received any official confirmation on Android 5.0 Jelly Bean other than a few hints at the recent MWC, but there is already talk about the codename for Android 6.0 going around.
Google has been moving along the alphabet with their desert names for the Android operating system with Gingerbread being followed by Honey Comb which was recently succeeded by Ice Cream Sandwich. So it would make sense that Key Lime Pie is the next desert in line considering it's popularity.
The report also sites it's source as being the same one who predicted that Android 5.0 would be named Jelly Bean, so we can assume that this prediction may also be true.
In any case we are a long way from Android 6.0, as Google has still to reveal any information on Android 5.0 Jelly Bean. Currently Android (4.0) Ice Cream Sandwich is barley trickling it's way to older devices with a very small share of devices compared to Gingerbread.
source - The Verge