Hi Xonox,
We don't have any plans to develop and Air version of BigBlueButton -- to install any software on a computer you need administrator permissions, and to distribute an installable application you must educate people on how to install it, ensure they have permissions to install it, help them override their virus checker software, test the installer on a large combination of OS, and notify users when updates are available.
The last point is probably the hardest -- once you have users install a version of your product, it's frozen. If a user doesn't upgrade, then you are forever supporting the earlier versions on the server. In contrast, you can update BigBlueButton on your server and everyone will be using the latest client.
Installing software has its positives, but they are far outweighed by the negatives.
Regards,... Fred