There is no direct replacement, they are just going a different route.
Currently if you take the 70-643 and have the 70-640, 70-642, 70-647 AND a client exam you then have an MCITP, which has the same upgrade path to an MCSA as just an MCSA 2008 has.
I've read about half of the 643 book - it has some great information and details software implementation very well. If you are doing that in your job i'd suggest reading that regardless of if you are going to take the exam. If your end goal is
just the certification, skip that one as there is no direct replacement in the 2012 certification list.