I found this article while doing a search on Exchange 2013. this article goes thru the system requirments you will need before you install Exchange 2013. I would check this article again when the release of Exchange 2013 gets closer to see if there was any changes. But for know it will give you a heads up on what will be required for you to make the change.

Before you install Microsoft Exchange Server 2013 Preview, we recommend that you review this topic to ensure that your network, hardware, software, clients, and other elements meet the requirements for Exchange 2013 Preview. In addition, make sure you understand the coexistence scenarios that are supported for Exchange 2013 Preview and earlier versions of Exchange.

http://technet.microsoft.com/library/aa996719%28EXCHG.150%29.aspx