seeming to just hang upon presentation; no keyboard pop-up or input but I could cancel/close just fine.MFMailComposeViewController
Sorry, here's the fix:
REBOOT THE DEVICE!
What I found most troubling was that all my recent (64bit) updates for my Cocos2D games have a "Contact Developer" button which of course opens a new message pre-filled out and THEY ALL WORKED FINE. From a coding perspective they were all the same so if one worked and others didn't perhaps I would have rebooted the device sooner. Nope, they all worked fine but my non-Cocos2D (UIKit) app was flat-out broken.
(1)by confirmed I mean I quickly found what sounded like my exact problems on stackoverflow.com and plenty of hits via google.