Well, they've done it. Mercury has partnered with MTT to produce a 400 hp diesel/JP4 fueled outboard motor.
It only weighs 380 lbs. It uses a Rolls Royce Allison 250 series gas turbine as the base powerplant.
It's still in design testing phase, and Mercury has no published plans to go into production. Here are some photos:
__________________
Common Sense is learning from your mistakes. Wisdom is learning from the other guy's mistakes.
Fr. Frank says:
Jesus liked fishing, too. He even walked on water to get to the boat!
Currently without a SeaCraft 
(2) Pompano 12' fishing kayaks
'73 Cobia 18' prototype "Casting Skiff", 70hp Mercury