InDesign CS5 SDK availble now.

http://www.adobe.com/devnet/indesign/sdk/

Adobe InDesign CS5 Products SDK

Adobe (May 2010)
Includes libraries, sample code, tools, and documentation for writing C++ based plug-ins for all CS5 versions of InDesign and InCopy.

• InDesign CS5 Products SDK (version 7.0)
• InDesign CS5 Products SDK Readme (TXT, 12k)
• What’s new (PDF, 73k)