I just got the word two hours ago:
“Hello Windows Installer (MSI) 4.5 Beta Testers!
This message is to let you know that we have just made the Windows Installer 4.5 Beta 2 build, tools and documentation available on Microsoft Connect. This is our last planned beta release before we ship Windows Installer 4.5, so your feedback is especially important at this stage. Please log into the Windows Installer 4.5 beta program on Microsoft Connect today to access the new bits!
– Tyler Robinson, Windows Installer Lead PM”
Go to http://connect.microsoft.com/ and subscribe to the beta if you haven’t already.