I don't see it so much as a "licensing a professional" issue, bur rather "licensing a public transportation system" issue. When one plans and dimensions the public transportation network of a metropolitan area, it must be clear which are the players and what type of services they must provide. Up to now, UBER does not follow any obligations that taxi unions must follow in any big city. For example, guarantee a minimum number of cars in the night, or holidays. So, if UBER wants to become a new taxi company (which is exactly what it is), so adhere to local regulation.