It'd certainly be a great idea, either for an upgrade or for a new "supercruise specialist" ship. Ideally the former.
The only thing is it would be such an obvious 'must have' upgrade, that you might need to counter it slightly to avoid it being the one upgrade every single Cmdr goes for. Perhaps one mod that increases acceleration and decelleration (but greatly reduces the max SC speed on longer runs). One SC mod that increases the max speed on long runs (but decreases the acceleration/braking; or is affected more by gravitational wells) and a third which greatly improves FSD performance in gravity wells / near planets (but has lower acceleration/top speed elsewhere). Then you'd have 3 great options. One supercruise mod for short range runs, one for long runs, and a third for greatly improved planetary landings/take-offs.