Maybe she's a cameo character.. Though, I don't really remember seeing her in the background anywhere. The only cameo I really remembered seeing before her actual introduction was Derpy. To me, she was obvious even without the derp-eyes. So I'm pretty sure I would've noticed this Skyla- Especially if she's a unicorn princess

Though, I don't think she's a future character.. Do you really think Hasbro would make merchandise off a character that was never even revealed in the show yet?... It's possible, but, I think she's just one of the fair assortment, like Zephyr said, from ponies just for kids to buy.