Found via Mark Harrison, Ryan Donovan explains why we won't be seeing a new MSIB. Basically because the gaps that existed before, and made MSIB necessary, have melted away due to better architecture.
Round of applause to ASP.NET 2.0 and Windows Server System Common Engineering Criteria (WSS CEC).
With the next generation you don't have to be part of the club, just make sure you read the docs.