I have to figure out how the CMIS support in SP2013 foundation does work out. And everything I find says that it is natively supported. But the site feature 'Content Management Interoperability Services (CMIS) Producer' does not exist. So I downloaded and installed the trial version of SP2013 Standard Edition and there it is... Already found out that the CMIS Producer was not a part of the preview but I installed the RTM release. So is it like in 2010 that CMIS is only available for Standand and Enterprise Edition? - because the site feature list says that it is also available for foundation (http://office.microsoft.com)
Edit: Called Microsoft support and there is definitely no CMIS producer in SP2013 Foundation (but in Server Standard / Enterprise). The agent also clarified that there is no difference in editon features between SP2010 and SP2013 (no CMIS Producer in SP2010 Foundation = no CMIS Producer in SP2013 Foundation).
Thanks to everybody helping investigate in this