If the bag is wide enough you can usually squeeze in something a little bigger than advertised with the board on an angle as it goes in. But it will push against the padding and not be as protected.
i have a cabrinha av8 bag - this photo is with a 5ft surf board, pocket foil board, three kites, 2 bars, foil, harness, pump and wetsuit. Both boards and all the kites are in their own bags and still fit with space for essentials (towel, boardies and a toothbrush


)
They are supposed to be for the cabrinha system but its just a regular (giant) roller bag. It would work well for a wing board as its quite wide (I haven't tried putting one in though as i'm riding a 6'3 sky sup!)