The obvious questions are:
- How are you going to cool it? I would imagine that we're looking at a large radiator, a lot of water, etc.
- How much does it weigh? Especially once you add the water cooling.
- How will you connect it to a propeller? Most propellers are happy around the 2500 - 2700RPM mark, which is also where most aviation piston engines operate. You can add gearing, but that adds weight, adds a point of failure, and potentially requires a flywheel to smooth our torque on the gears.
- Can you get it certified and persuade an aircraft manufacturer that it's a valid option?
With regards to lifespan - suppose you put this in a car, hooked up a massive trailer that will require 500hp continuously, and went for a drive on the highway at 100km/h. How far do you think you'd get before the engine needed an overhaul? 1000km? 10,000? 100,000? I'd be guessing somewhere substantially less than 100,000km. But that's only a thousand hours of use, and most aviation engines are very conservatively rated to at least 2000 hours before overhaul.