As Sykes says, we actually already have a crude incremental throttle system, in that the ships don't decelerate by themselves. So if you ease your speed up to, say, 60, and let go of the W button, it'll stay at 60.
Very useful when you've got slower ships in formation with you.
"One of the bitches actually gave birth while she was attacking, and her puppies joined in on the carnage."
--the awesomeness that is Boatmurdered.