Currently, InCopy ICML is the file format that Bookalope supports as an export format for InDesign. However, a closer integration with InDesign would be great and we are now looking into two different options.
Each option has its pros and cons. What, in your experience, would be the most useful and desirable option from a user's perspective? Is running a script too cumbersome? Is XML access secondary?
IDML option seems better. If you already have your publication content in XML then just apply XSLT to it and generate the IDML. As you already use IDML approach for ICML generation, this would be a consistent approach.