The problem here is this: Luna can not, and will not, turn bad.
Why? This is a children's show that is trying to show lessons of friendship. Luna already wanted a second chance, her throwing it away and being a bad-character would send a bad message to kiddies. The lesson is second chances, redemption, redundant-other.
so it's a predictable story. I mean, she ruled with Celestia for a long time til she got jealous. she had a good nature until that point, it'll return.
I want Discord back. :C