We've got some good news for those of you who missed out on the boxed set of Daring Do books (or didn't want to get all at once)! Amazon has a pre-order listing for The Marked Thief of Marapore which will be released early next year.
Thanks to Stardreamer for sending in the info.
My Little Pony: Daring Do and the Marked Thief of Marapore
Twitter: Calpain