I haven't seen such a beast, and I suspect that's for a good reason. Normally you would "finish" using a boat diesel by dropping into neutral and then letting the engine idle for a few minutes--never simply shutting it down.
That accomplishes a couple of things. It gives you time to shut down the electronics
before the spike gets thrown by the alternator
shutting down, and it allows the engine to cool down and throw fresh (cooler) oil
around internally. And it allows the blower (if you have one) to cool down the enginge compartment some.
Having one control? Handy, but you still need
a totally separate and redundant way to kill the engine--even if your throttle or transmission
cable has jammed, as they eventually do. This could be one case where "less is more" just wouldn't apply.