this article does a fair amount of discussion on advantages. Basically it is quiet, has no on-site emissions, and is theoretically more efficient. They also go on to mention that it loosens some design constraints. http://www.technologyreview.com/news/516576/once-a-joke-batt...
Those wouldbe advantages of an all-electric aircraft, however this article is not about that. This article is about an electric motor that could be used in a series-hybrid aircraft, that is, one with a fixed-speed combustion engine and small battery or capacitor.
The original article mentions hybrid but does not say the motors are exclusive to hybrid drives, merely that the motor will be flight tested in a series-hybrid DA36. Besides, the MIT article I linked enumerates the benefits of the hybrid drive. The word 'hybrid' is in the subtitle. I suspect Siemens is focusing on hybrid tech at the moment because battery tech is such a moving target and they want to use an existing airframe. Ultimately, I think all-electric aircraft will find their market in short-flight urban transport applications where noise, pollution, and reliability are huge factors.
