I don't think Cocina Mexicana is that bad. I mean, pretty much always have lower standards for theme park food... and on that relative scale, I didn't think it was bad.
And I believe I said this before, but we ate at Antojitos in Orlando and found it... fine. Not great, not bad. Fun atmosphere, but only fair food. So I'd suggest lower your expectations, and you'll be fine. That said, while I support family owned businesses, I never thought the food at Camacho's was all that great... very "meh."
In any case, when asked at the door, they said it would open to the public on Aug 22. It's currently invitation only soft opening.