Isn't that idea what Hinkley Boats now have? A 2" line fore and aft should get you started (Kinda like Red October). Reverse could be done with two "Y" valves to reverse the flow. You could even go wild and throw in the bow thruster lines. If you could keep the lines cleaned out it would be impressive.
All U Get
Interesting thought if I must say, at least for bow thruster power. Check valves might work to keep it "clean".
Regarding jet pumps, though, efficiency is always highest when moving a large volume of fluid slowly, and lowest in efficiency when moving a small volume of fluid rapidly. Jets only win in purchase cost because they are cheap. There is as yet, not a more efficient means of propulsion, in water (or air), than a prop.
