Air cylinders on a car that uses a strut suspension isn't very safe. Not only will you risk breaking a shaft or the cylinder, but they will wear out VERY fast. Once the seals are loaded up and then you force them to turn they will wear out. The side loads that a strut goes through is nowhere near what a cylinder is designed to handle. THe body of it can start to balloon. Ive tried it with a Parker Xair cylinder that EAI developed years ago. Here in NY, they wouldnt hold up for over a month. It was a pain to replace them so we just went to the UAS aero strut bags. They slip right over the factory strut. You may be able to use them with a shorter bodied strut to get even more drop than the factory strut will allow.
Check out Praxis. They make performance air suspension systems for vehicle. I know they make them for the older subarus but you can call and find out more info.
http://www.praxissystems.com/