Yup been used for ages on bikes. Not sure who did it first but Yamaha have had the ExUp valve for a fair few years now. All done electronically. Astons also have them, as do a few more exotic cars. I beleive it keeps back pressure up at low revs, then opens at higher revs to be more free flowing and also gives some more noise
Oh also, it would only be of use on more high flowing exhausts that dont provide enough back pressure at idle. You would need something specifically designed for the valve. Would be good though, as at idle it would be nice and quiet, then at full throttle when the valve fully opens all hell would break loose!