Content Type Association with SharePoint 2013 Workflows

In SharePoint 2010, when creating Reusable Workflows, there was the option to associate the Reusable Workflow with a specific content type (as shown below):

However, with the release of SharePoint 2013 and SharePoint 2013 Workflows, for unknown reasons, this capability has been removed!

Therefore, when creating a SharePoint 2013 Reusable Workflow, there is no longer an option to associate the workflow with a specific content type!!

As you are re-writing your workflows for SharePoint 2013 (when coming from the SharePoint 2010 platform), this is one major point to consider.