A simple valve operated via cable would be nice. Also if targeting a performance market, a larger ID would almost be a necessity.....
You know you don't have to put the thing ahead of the turbo right?
The flow rate post turbo and post intercooling is much, much less and should be the place to put the valve. Then you might stick a cheap blowoff valve between the charger and the cutoff so the charger(s) wouldn't bark or tubing/intercooler wouldn't pop when the valve closed suddenly downstream.
Doing it this way would also prevent an uncontrolled runaway if the engine blew cac piping before you got the valve engaged. In a situation like that, running a cutoff valve pre-turbo would do nothing as the engine would be pulling air through the blown piping downstream of the valve.