He has a simply supported beam up there which will have significant stresses trying to counteract the loads on the fore and aft stays and the halyards. He even states that he needs to lengthen the upper gaff since the sail comes in contact with the mast on the unfavoured (port) tack in the video. I'm sure he kept it as short as possible to minimize loads. Lengthening it will add significantly to mass at the mast head which is always a bad idea. The mast isn't completely out of the air flow but holding it away from the sail should help some. I can see the ease of use and clearer air being an advantage but the weight up high might over ride the performance advantage. A lot of high performance boats have foil shaped masts which would negate a lot of the advantages of this rig.

Even though I'm being a little pesimistic it's always great to see inovations in sail design.