It's already been said by others, but I'm going with the idea of an upgrade Ace-level detector that's waterproof.
It might even be mutli-frequency, too. But won't be using tech as advanced as Multi-IQ. I'm guessing any multi-frequency feature will be more of a marketing gimmick.
My second guess is that it's a new flagship detector with price drops of the AT Pro/Max (and maybe even dropping one of those machines altogether).