| yes , this can be used to classify individuals who have been assessed .. you can use the 9 box for succession planning, leadership identification and even for performance appraisal. My recommendation would be that you use the model after performance appraisal so that you can look at see who are your stars and who are your future stars and who are your laggards ...
if your organization uses performance criteria like ratings on behaviors, work skills, delivery etc, you can use that as criteria ...
My recommendation for assessing potentials is to use behaviors, functional and technical skills needed for the role and then compare your individuals against it ... this will give an idea of how close are they in terms of fitting the promotion role into the future ...
if you need more help, let me know | 
