I've finally found a video about the new dolls, which is actually kinda informative. I picked up some neat details I hadn't head before.
The guide says:
Rarity has a Crystal fashion show, the Bohos vs. the Geometrics. Is this a hint that we'll see a friendly competition?

Next, she says the girls pony up and grow crystal wings. I'm assuming she's only talking about Twi, Sunset, and Dash, but it's interesting Dashie gets special crystal wings!

And finally, she says the Crystal Gala will be located in the Crystal Cave.

"They go to Camp Everfree, mysterious things start to happen, so... is it the legend of everfree? I guess we'll have to wait and find out."

So what is the legend in question?

5076378

I'm assuming she's only talking about Twi, Sunset, and Dash

There's too many alicorns, somepony had to sacrifice their wings for the greater good.

5076378 I can feel the hype

5076451 Well I know what direction my story's going in now.

5076378

Ooh, nice!