When A is clearly depicted, even word of author can not make it B.
Rarity WANTS to be an Alicorn Princess, it's pretty transparent, it's the final embodiment of her desire to rise above her starting points. But Twilight, who never wanted ascending, is the one to claim it.
I'll answer this: The bearers of the Elements of Harmony have recently became alicorn princesses. I know that may sound weird for some fans, but I'm sure being in a top rank and having the gain of wings and horns would come in handy.
Also, yes, I guess you could imply that Spike has or is nearly going to marry Rarity, she's giving her little Spikey-Wikey the ride of his life.