In the 1960s, Popular Science (I was young and didn't know any better) had an article about the benefits of an experimental active suspension -- all hydraulic. An idea whose time had not yet come, it never made it off the magazine cover. In the 1980s, formula one cars (Lotus) combined computer control, incredibly fast valves and high pressure hydraulics to make very effective active suspension. So effective it was banned in the 1990s. My company sold very expensive high speed digital storage oscilloscopes to Lotus and others for developement, setup and repair.
Autozine has a brief history of active suspensions.
Now, Bose is getting ready to sell the automotive industry more than audio. After a claimed 20 years of development (I'm guessing that not many were front burner years), they are showing very impressive videos of a computer controlled system that uses electromagnetic linear actuators to deliver great handling and a luxury ride.
Like ABS, traction control and stability systems, if it comes to market, active suspension will not be cheap. It will be offered first on high priced luxury and performance cars, eventually working its way down to the rest of us. Can't wait!
For the mathematically inclined, think about the differential equations that define the system. Is the objective to control the large mass of the vehicle or the much smaller "unsprung mass" of the tires, wheels and brakes?