All the normal sources I'd use for reliability data don't include the diesel because it isn't sold in the US. Fortunately, I live in the US, so that's not a choice I need to make anyway.
Given the contortions VW is having to make with their latest diesel, I'm inclined to think that if Mazda brings a diesel to the US, we won't be able to assume it'll be as reliable as the diesel they sell elsewhere. At a minimum, the exhaust system will probably be quite a bit more complicated.
Mazda is having too much issues with excessive fuel in the oil for me to even consider it at this point. When Mazda get the problem resolved correctly, they may bring it to the US. Ed