I've actually thought about the idea of doing a tank like that someday. My idea though was to make it square, say 5' X 5', with a drilled bottom and an overflow in the center with rockwork around it to disguise it.
I would imagine that it would be possible to go braceless so long as you increased the thickness of the glass. I'm not sure how much you would need to increase it by but it would stand to reason that with less support thicker material is needed. Another option might be to make a top brace out of some nice 3/4" hardwood plywood finished to match your floor. With some creative scroll work it could actually add to the look of the tank as well. A matching hung light fixture would probably complement the whole thing nicely too.