On a Microsoft Connect post is was specifically asked and as usually Microsoft came out with a definitive - " The current target is Q4 2010"
So based on when Microsoft SQL Server 2008 R2 came out in 2010, you should see SQL 2005 SP4 around 2012
Sorry for the sarcasm, Microsoft can be frustrating.
Chris Powell
George: You're kidding.
Elroy: Nope.
George: Then lie to me and say you're kidding.