Spec,
Spillover from FB is expected next year in my opinion because F2A is current but its processing is super slow at USCIS. These are the dates from USCIS:
https://egov.uscis.gov/cris/processTimesDisplayInit.do
Field Office Processing Dates for California Service Center as of: June 30, 2013
I-130 Petition for Alien Relative Permanent resident filling for a spouse or child under 21 November 15, 2011
Field Office Processing Dates for Vermont Service Center as of: June 30, 2013
I-130 Petition for Alien Relative Permanent resident filling for a spouse or child under 21 June 4, 2012
Cases after these dates may have been processed but in general it indicates very slow processing by USCIS. So even after making F2A current, I think it may not generate a whole lot of demand. So there will be lot of unused numbers in this category.
Now whether this gets used through Fall down to other FB categories or be transferred to EB categories remains to be seen.
CO talked about setting a cut off date for F2A in October. this may imply that demand is greater than 1/12 of the quota after making dates current but it may not have been enough to use all of FY13 quota.