Well even if you can't transform into them having a creature underwater that is actually a formidable enemy would add to the game so you would always have to be on your guard... And who's to say they cant leave the water in wereshark form, I mean there's no real rules for what a mythological can and can't do.
Very true! When you put it that way, I'd love to see some weresharks chasing npcs up and down the beaches

Unfortunately I have to agree with the majority though, don't see this one happening.