I have no idea how I missed that this was even being discussed but it appears that talks have been taking place for some time now. It's all off the back of Skymark's botched order for 6 A380s. As a result of cancelling the order, they now owe Airbus a cool $1bn. But ANA saw an opportunity.
ANA would take Skymark's A380s and deploy them in the domestic Japanese market in a high-density configuration. Skymark would retain its own brand and operation, so the cooperation would extend beyond simple codesharing but stop short of a merger.
Airbus is hugely enthusiastic about this deal for obvious reasons; the order ultimately gets fulfilled, they don't have to put a small airline out of business, and they see the A380s fragile Asian presence grow.