And then there's this:
The new rules contain an unusual exception: the revised tax return deadlines do not apply to C corporations with fiscal years ending on June 30 until taxable years beginning after December 31, 2025 (however, the revised Form 5500 extension deadline does apply effective in 2016 to plans and corporations with June 30 year ends).
http://www.relius.net/News/TechnicalUpdates.aspx?T=P&1=1&ID=1072
(via http://benefitslink.com/newsletters/2015/2015_09_16_welfare.html)