pretty much the only martial art that where's gi pants under the hakama is aikido. in iaido, our jackets are longer... hides our legs from the opening in the hakama. then again, we don't take breakfalls or any rolls in iaido, so there's no chance of showing that we're going 'full metal' under the hakama...
Personally, I think it's a great idea. Living in Miami, the more air flow (big pants) and the less layers (no gi pants underneath), the better (especially during the summer).
Thanks for the information regarding Iaido, I had no idea. Never even stopped to think about it. Just assumed that everybody had gi pants on under there. Interesting. Learned something new. Many thanks.