Hi William,
Thanks for creating a post. At the moment, Subject7 does not support any non-relational databases, but there are plans in one of the future releases to add MongoDB. Please keep a look out at our release notes page to learn of future enhancements and new features:
https://subject7.zendesk.com/hc/en-us/sections/200570628-Release-Notes
Regards,
Subject7 Team