It dosen't have anything to do with RPing but I'd rather do it here than the TES wiki. The bosmer are supposed to be able to shapeshift because they witnessed the creation of the Earthbone.
In his passing, his spiritual energies formed an Earthbone, a natural law, to limit certain aspects of the world. Yffre's Earthbone placed a limit on the ability of a being to change its form and nature, as previously they could change them at will. However, the Bosmer, having witnessed the formation of the Earthbone, learned how to manipulate it to avoid its restrictions.
But they can't. (Dam you,Bethesda!) But if the next game was in Valenwood, maybe the player could gain the power of shapeshifting.You wouldn't have to play as a Bosmer, much like how the Dragonborn is supposed to be a Nord but can be other races.Instead of fighting a dragon to get a different shout, the player could fight the spirit of the animal ( About as powerful as a dragon.) to gain a new form.
I think if they ever made a game in Valenwood, they would make more creatures, which would make this ability more fun than killing dragons. Dragons are just the same old thing all the time and most players kill dragons with ease. Each form could have different abilitys, like a fish could breathe underwater, a bat had permenant night-eye and detect life, a hawk could fly like on dragon back, a skeever could fit through small spaces etc.
I have no idea how this would fit into story or whatever, it's just an idea, I'm not making a game.