I'd like to push the idea further from a knowledge management/organizational learning perspective. There have been arguments for including "learning" metrics in individual performance assessments. The (simplified) logic is that if you want to encourage t a particular behavior, you should measure it.
I'm not sure if there is research on this topic (I suspect there is), but my intuition tells me that while performance monitoring may be useful to identify and take action on under-performing employees, it is much less useful in rewarding high performance employees who are self-motivated in the first place. You might force under-performing employees to comply with certain things by threatening them with bad performance assessments, but can you force an under-performing employee to learn more? I doubt it. Can you help a willing learner? Yes, but adding a learning metric to their individual performance evaluation won't do it.
So, here's the question: How would/could a learning metric have a positive impact on employee learning? Perhaps indirectly, by communicating the organization's recognition of learning as an important element of performance; by forcing conversations about what constitutes workplace learning, what is an effective learning strategy for individuals.
If the ultimate objective is to have these ongoing conversations about workplace learning and how it contributes to individual, team and organizational performance, then individual performance metrics may not be the most appropriate starting point. They may be a minor component of a much broader strategy (see map below).
This also illustrates a point made by Beer, Finnstrom and Schrader (2016) in "The Great Traing Robbery," which is that training -- and leadership development in particular -- needs to be fully integrated with organizational development.