Alternately, it could hypothetically give you more IOs for an existing RPi over USB ;)
On another note, I'm pretty sure your particular dual-licensing scheme is invalid; the GPL does allow commercial use of a thing licensed under it, so people hoping to "produce it and sell it" would be legally able to do so (though perhaps with a bit of indirection, like forking it under the GPL's terms as a "personal" project, leaving out the commercial restrictions (since enforcing them would be a GPL violation), then letting someone else thus use it for commercial purposes without restriction (other than the GPL's copyleft requirements).
Unless by "produce and sell it" you mean "produce and sell it under non-GPL terms or without schematics", in which case that is acceptable and useful. In any case, clarification would be wise.
On another note, I'm pretty sure your particular dual-licensing scheme is invalid; the GPL does allow commercial use of a thing licensed under it, so people hoping to "produce it and sell it" would be legally able to do so (though perhaps with a bit of indirection, like forking it under the GPL's terms as a "personal" project, leaving out the commercial restrictions (since enforcing them would be a GPL violation), then letting someone else thus use it for commercial purposes without restriction (other than the GPL's copyleft requirements).
Unless by "produce and sell it" you mean "produce and sell it under non-GPL terms or without schematics", in which case that is acceptable and useful. In any case, clarification would be wise.