In the discussion in the SAP BPX Community many users stated either directly or indirectly that a BPX needs to have experience. Which means (sorry, youngsters) that not a freshly graduated alumnus from college or university can fill out this role, but mostly senior people with multiple years of professional experience, ideally from different industries or departments within an industry.
Experience is not only the familiarity with tools and methodology itself, but perhaps what this aspect describes more is the soft skill of knowing about internal structures and networks, politics and rivalries, who has to be involved to get things done, knowledge about the history of the business and processes, the people, the IT systems and landscape etc.
This also implies that due to your own history and past, you might not be able to become a BPX in your current organization or even industry (it's a small world). Your reputation might have been damaged with the very same people that you need to collaborate as BPX. This does not mean that you should shy away from conflicts, as long as they are fact and evidence oriented and not based on prejudices and attitudes. It simply tells you that you should always act in a way that allows you working with the very same people in a constructive way again.