Sure, and an engine that wouldn't need any fuel/power at all would be even better - the question is, what is practically/theoretically achievable. But I guess

Sure, and an engine that wouldn't need any fuel/power at all would be even better - the question is, what is practically/theoretically achievable. But I guess the fact that everyone is avoiding the elementary question of 'how much can a transportation system transport' tells me all I need to know about the practicality here.