Comment by jebr224

There are two standards for pluggable BMC's

  - runbmc (https://www.opencompute.org/documents/ocp-runbmc-daughterboard-card-design-specification-v1-4-1-pdf)

  - DC-SCM https://www.opencompute.org/documents/ocp-dc-scm-spec-rev-1-0-pdf

I have only glanced the surface of these specs.