I believe this has a lot to do with curved boards.

While there has been power and apparent angle to trap out downwind, the a-cats just haven't had enough buoyancy to support it. Heck, that's part of the reason the wild-thing is so important to do well on the a-cat downwind. In moderate breeze, the wild-thing helps to unstick one hull and make it quicker...more apparent breeze at deeper angles. When the wind is up, wild-thing is a survival technique. With your weight in the middle of the boat, righting leverage is decreased which reduces the amount of pressure the leeward bow has to support. Less pitchpolling is faster.

With the introduction of curved boards, the sailor gets a chance to manage the amount of lift the leeward hull/foil is generating with his weight position fore/aft and now trapping downwind is possible. It's no different than trapping downwind with a spinnaker really.