No out of the box integration like ACS is supported by Adobe and there currently are no plans for one. That said, with the help of Adobe consulting or one of our partners, ACC can be used in two primary ways:
Adobe Campaign Classic could be added as a data source to read profile information. Adobe Campaign Classic API format uses SOAP and XML. This requires a solution using Adobe IO Runtime to perform the API request and data manipulation between Journey Orchestration and Adobe Campaign Classic.
Adobe Campaign Classic Message Center could be added as a custom action. Again, IO Runtime would be needed, see above.
Note that the volume of API calls to Campaign should be throttled to avoid overloading the Campaign server.
Note that beyond these two API based integrations, consulting or partners could come with other solutions.