The InDesign update you received in August 2013 (InDesign 9.1) included the enabling of HTML5 extensions.
As you may already know, starting in the middle of 2014 Adobe will begin removing Flash-based extension support in Creative Cloud products, starting with Photoshop CC.
If you have any hybrid or regular Flash extensions for InDesign you need to begin migrating them to HTML5 as soon as possible.
As you may have noticed, the InDesign CC SDK is available by request from http://www.adobe.com/devnet/indesign.html.
In this latest release we’ve added new samples to the SDK whilst some more basic features of plug-in development have also changed. We’ll talk about the new samples in future blog posts, but find below the more fundamental changes you need to know about if you are creating plug-ins for InDesign CC.