We have had very surprising nominations (of newcomers into roles that were previously held by well-established and competent partners), and subsequent nomination changes (more people joining the nomination of the newcomer), and, sometimes, objections of the nominated newbie on the grounds of "I don't feel experienced enough to hold the responsibility". These could be integrated by supplying a coaching structure for the newcomer.
In response to your question, "how do others get experience or demonstrate their own capacity?", two things come to mind:
- they can nominate themselves
- you can nominate them, making a case why they should be given a chance (knowing that elections can be called by anyone at any time - this has often been argued in our circles: "yeah, well, let's give them a chance; and if you mess up, we'll just elect someone else. ;-))"