My trusted parts man at the dealership says that the quality of the SkyActiv drivetrains has been excellent.
The concern with Mazdas here was not the mechanicals so much as the bodies - they rusted incredibly fast from about 2000 to 2004, not as quickly but still badly until about 2009 or '10.
I have not seen a rusty 2012 Mazda here so far. We're not in the worst part of the rust belt by far, but it's always a concern here.