Found this vid for an Exocet foilboard with apparently tandem foils
Can't see that they've done any development recently on the idea, BUT, thinking out loud here.
I have a couple of Starboard boards with a center fin slot -tuttle box. Looks like they could be the ultimate light air machines with a couple of foils. Not speedy with the extra drag but enough lift to foil on not much wind at all.
Now to pick the winning lottery number to fund my idea. 
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Why stop at 2?
What happens in a black hole stays in a black hole.
Because .... that's how many fin boxes I have? Besides, apparently three foils only work if you where a farmer john style wetsuit which is the wetsuit equivalent of the mullet.