Q,
I do sense something is afoot.
Here's the history of the previous Extension Memos and their publication dates (as far back as I am going to look anyway):
July 23, 2003 - extended until January 1, 2004
January 8, 2004 - extended until January 1, 2005
December 2, 2004 - extended until January 1, 2006
January 11, 2006 - extended until January 1, 2007
January 3, 2007 - extended until January 1, 2008
January 7, 2008 - extended until January 1, 2009
December 10, 2008 - extended until January 1, 2010
December 30, 2009 - extended until January 1, 2011
December 16, 2010 - extended until January 1, 2012
December 29, 2011 - extended until January 1, 2013
December 20, 2012 - extended until September 30, 2013
September 4, 2013 - extended until May 31, 2014
In recent years, apart from the last extension, they have been published well before the previous extension expired.
The last 2 extensions have been for a period of less than a year.
Even though the last extension was published very close to the expiration of the previous extension, I do not remember USCIS issuing RFE requests, or AILA suggesting the policy might change.
I can see 2 possibilities:
a) USCIS will (eventually) publish a Memo with a fixed validity period from the original examination that they will accept.
b) USCIS will no longer extend the validity and fall back to the 1 year expiration date.