I recently did an interview at the YA Promo Central website. Here is an excerpt of that interview:
YAPC – How many more books can we expect in this series?
Jeffrey - I have already written the sequel to Mary of the Aether and signed the contract. It is called Mary of Shadows, and it comes out next summer from Whiskey Creek Press. It is much more intense than the first book, and I can’t wait for people to read it and see the crazy things I have in store for the characters. I have also worked a bit on the third novel in the series, which is currently called Mary of Starlight (but the name is subject to change). I expect the series to take four books to complete, but we’ll see.
Find the rest at http://yapromocentral.com