According to a new report by Japanese blog Macotakara, Apple is testing internally a new version of the MacBook Air powered by an ARM-based A5 processor and Thunderbolt connectivity. The website reports the machine is made by Quanta Computer, and this speculation comes amidst rumors of a MacBook Air refresh featuring Intel’s Sandy Bridge and Thunderbolt set for a June or July launch.

According to this source who saw live A5 MacBook Air actually, this test machine performed better than expected.

Though it’s not clear which Mac OS X or iOS is pre-installed on this A5 MacBook Air, iOS seems to have difficulty to use features of Thunderbolt without Finder. And even if Mac OS X is installed, developer should spend time to support A5 on Universal Binary Applications. As considering these situation, this A5 MacBook Air seems to be made just for experiment.

The shift to an ARM architecture on OS X would require Apple to rewrite parts of the operating system (though iOS, derived from OS X, runs on ARM chips) and, most of all, third-party developers to update their applications to be universal binaries capable of running both on Intel and ARM CPUs. This would be a resource and time consuming process according to many, similarly to when developers had to switch from PowerPC to Intel years ago, though a recent report claimed that Apple was willing to implement ARM on the desktop, perhaps also offering converting tools and other utilities to make the transition easier. Still, Macotakara seems to suggest this alleged A5-powered Air is being tested as an experiment, which, if true, wouldn’t come out at least until next year; the website correctly pinpointed many of the iPad 2 hardware and design features in the past months, offering credible mockups of the device ahead of its launch.