Good point. Shining would be a good one as well, because I already figured out he'd probably be the next alicorn if alicornism won.

1) He's a very skilled unicorn, so he can transform other alicorns. 2) He has a strong relationship with not one, but two of the royal alicorns. 3) He's very important in the defense of the realm.

Hell, I'm pretty sure Shining is technically a prince now anyway. It wouldn't be much of a stretch, and he could certainly appear in the same settings as the other four where other potential characters can't. (Say, eating at the royal dining room at Canterlot Castle.)