Golden Russet's Twitter page right now.
First off, following various replies, it looks like the voice actor for Luna will be returning; even though she only has one line and a "gasp" in the second episode of season 1.
That one line did fit her really well though! I'm glad for this.
We can also conclude that Season 1's Voice Actor auditions started on June 1st. Apparently there were a bunch, based on Golden Russet's tweet: "Tired from a full day of casting ponies. So much to choose from!"
Hopefully this means we will see more new characters, and not replacements to current ones!
Also buried a bit deeper is some very...interesting news. It looks like Goldenrusset is trying to get Powdered Sugar into the cast of MLP, by way of cookie bribes.
Thanks to HunterTSF for the heads up!