Which supporting ponies in FiM would you promote to a main pony in G6?

[eddeams 66]

In G3, Sweetie Belle and Cheerilee were part of the main cast. But when G4 rolled around, they were demoted to supporting characters. Which supporting pony from Friendship is Magic do you think would be a good member of the Mane Six?

Personally, I'd love to see Princess Cadance as a main pony. There's a lot of potential in her I feel G4 hasn't realized.