Could you please share some strategies or advice on how to promote greater leadership and ownership of projects within volunteer communities?
I think, in its essence, leadership and ownership is just another way for users to contribute to the success of the community. Taking on this kind of responsibility means upping the stakes in their participation in the community. Only super engaged users can take on this. As a result, the answer is prosaic: to nurture leaders among the users you need to work on engagement. Here are two things I would recommend to think about in this context.
The first is the so-called “sense of belonging”. I define it as a degree to which a person sees themselves to be connected to their community and satisfied with their role within it. Sense of belonging emerges through constant positive interactions with other members of the community. To boost it you need to make users get to know each other and work on something together. The more they do it as a group, the more responsible they will feel for the success of initiatives they are working on (or even suggesting themselves).
The second ingredient of the secret sauce is communication. You need to make users act in the first place. Step by step. It requires communication. A lot of persuasive communication and asks. Talking to users, presenting goals, suggesting initiatives, etc.