I believe this has to be established by the member of the Mozilla staff that would be directly working with said “leader” perhaps with a bit of input from the community that the would be “leader” will be leading.
I would also say that the Mozilla staff member most closely working with a “leader” shall have powers to enforce these standards and maybe some public or anonymous mechanism that the community could use to flag when a “leader” is not fulfilling or maybe even overstepping the “leadership” position (s)he holds.
How about a small set of KPIs that the member of the Mozilla staff that would be directly working with the “leader” establish with input from the community that should minimally be met. Some form of way to “sound an alarm” shall be also be provided to the community in case something goes sideways or really wrong, maybe even inclusionmozilla.com or similar.