I think Upwork can do what Freelancer.com did, and that is to add skills to jobs, and when someone completes the job, it adds a point to that skill. For examle I have skill Linux, and when I finish a job that has linux skill requirement in description, i get certain amount of points to my Linux skill, so it says Linux (5) or so. When I get enough points on some skill, that skill is exluded from skill counter, so I can then have 11 skills added to profile and not 10. If all 10 skills have points, I get to put 10 another skills which are not pointed. Like endorsment on Linkedin.