Probably late and shared with a dozen others, but this is my idea on how Twilicorn's going to play out.

Ep 1. Magical Mystery Cure. Twilight becomes Twilicorn.

Ep. 2. Twilight is enjoying Princess life, but finds that she misses her friends/Princessing has downsides as well as upsides/etc. This revelation comes just as a GREAT EVILtm threatens Equestria.

Ep. 3. GREAT EVILtm is defeated, but Twilight has to give up alicorn powers to get rid of it. She opts not to gain it back (if offered), preferring her Ponyville life to her Princess one.

In any case, Twilight turns back into unicorn, aesop about how becoming a Princess (gaining massive power, achieving a dream, some crap like that) doesn't really make you happy, but friends (magic of Friendship) do. Kids get a nice message, bronies can stop raging, and the 2uni:2peg:2earth ratio is restored.