For anyone who didn't click through and read the linked post carefully, it went back and forth and one of the final posts was this (my emphasis):
http://www.relius.net/News/TechnicalUpdates.aspx?ID=468**************
Short 2009 plan years. The 2008 Form 5500 instructions indicate that plans with a 2009 short plan year which have a 5500 filing deadline before January 1, 2010, may file a paper 5500 using the 2008 forms or are eligible for an automatic extension of 90 days following the date electronic filing becomes available. The result of this policy is that plans with short years having a deadline after December 31, 2009 (e.g., plans which terminate after May 31, 2009) have no option but to wait for electronic filing.
DOL and IRS officials seemed surprised by this result and indicated that the DOL will not reject a paper filing for any plan with a short 2009 plan year, regardless of its deadline.**************
Looks like the 2008 Form 5500 paper filing will be accepted... in all cases regardless of the deadline/due date. (amazing that DOL was surprised, when they are pretty explicit on their website summary)