It looks as though people might have jumped the gun a bit in regards to whether or not Google will debut Android 5.0 at Google I/O. According to some leg work done by AndroidPolice, it's much more likely that Google will debut an updated Android Jelly Bean version at I/O going by the version number 4.3.
A build going by Android 4.3 JWR23B has been showing up in their server logs. They then traced down the IPs that they were coming from to Google. More specifically, AndroidPolice claim that the IPs are associated with two employees that are heavily involved with Android.
The build has been showing up on Nexus 4 and Nexus 7 devices. Typically, Nexus devices are the first to get a new version of Android. Finally, AndroidPolice cites several bugs that have cropped up in the Chromium bug tracker that list JWR23B as the build.
We'll know for sure as soon as Google I/O happens in about three weeks.