well... they've been developing this new package especially for the Monaco GP, and I don't think they'll ban it actually.
Williams and Minardi have formerly driven with such a wing, which I think is to get a little more air down under the rear wing elements to be pulled up right behind the rear-wing elements.
Anyway, this is just tipical Monaco design, the extra wings, it's odd if you don't add something special
. Nevertheless, I don't think this helps a lot, we'll see