I don't think it would matter too much, actually. You're already elevated off the floor in the B&M "hyper" cars (probably the most comfortable seats on any coaster, at least to my body, closely followed by the cool unique PR trains...)
Not that I wouldn't want to TRY it, mind you. Just noting that people already dismiss floorless coasters as gimmicks (missing the point that they're still B&M sitdown loopers -- never a bad thing) and with those hyper trains, losing the floor would have VERY little impact.
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--Greg
http://www.pobox.com/~gregleg/