Just got finished with importing and testing the actual conversion code for the Mac version of BLPNG Converter, and everything seems to be in working order. At this point, the only real heavy coding left to go is converting the raw pixel data into the PNG format, and handling writing both to disk.

Now for some potentially bad news. The collection of code that does the actual BLP conversion, is written in C++. For whatever reason, in Mountain Lion's version of XCode - Apple has decided to only support C++ for OS X 10.7 (Lion) and newer. I had hoped to go as far back as Snow Leopard (10.6); but the benefit simply doesn't match up to the extra effort, in my opinion.

First off, the user share (among Mac users) for versions 10.7 and above, add up to an astounding 85.6%.
Second, Blizzard has listed 10.8 (Mountain Lion) as the minimum requirement for Warlords of Draenor
Third, OS X 10.9 (Mavericks) is free - so if your Mac can run WoW, there should be no reason not to have at least 10.7

So, 10.7 will be the minimum supported version with this.

It's also worth mentioning that, due to the nature of Photoshop plugins - namely the fact that they're not applications, and that they don't interact directly with OS X, the Mac version of the BLP Photoshop plugin may not face this limitation. The goal is still 10.6 for that.