I am delighted that you noticed the piece framework design.
The connectors have no dependency on the core. We are currently working on releasing each connector as a separate npm package, which can be utilized in any codebase.
If this is useful for your particular needs, or if you have any suggestions/ questions, please let me know.
If you are interested join our discord, we do the announcements there.
I'm literally half way through building something similar for our own saas.
Love what you are doing with authentication/connections to other services.