For some reason, Google has delayed the registration process for their Google I/O 2014. It was originally going to begin today, but instead it will now run from April 15th through April 18th. Here's a quote with the report from the Google Developers Google+ page: It looks like they are still organizing to make the process even easier. Sound off and let us know if you plan on attending this year.
The possibility of the Nexus 8 and Android 4.5 not appearing at the Google I/O is highly likely since the company will want the focus to be on their services and not products.