I think I'd prefer a code review discussion where the file being modified is a CSV file listing everyone in the organization's roles, seniority levels, and compensation, and where anyone in the company (and perhaps at a later date, outsiders) can comment on and view the discussion and file history -- both while the promotion review is in progress and after the fact.

(perhaps the inputs to the promotion suggestion could be from a documented and equally-open algorithm; I still think it'd be nice to have the results reviewed and discussed (openly, by humans) before they take effect so that potential unfairness -- either in the levelling, or in the algorithm -- could be addressed)