It might be feasible to assess a single contribution, but not feasible to assess all of them. To make this KPI work, maintainers would have to publish an object

It might be feasible to assess a single contribution, but not feasible to assess all of them. To make this KPI work, maintainers would have to publish an objective quality rating for each accepted commit. That's an enormous amount of work, and impossible to get right anyway since the value of a change might not be immediately obvious, or might be negated by a future change, etc. The advice to companies using this KPI would be: let your own dev managers evaluate the quality of the commits of their engineers, and rate them on quality as well as quantity, then submit. Engineers will quickly stop creating busywork when their managers get wise to it.