When sectors overlap, new niches form.
Initially, there is a period of chaos in these new niches. Nobody knows who the stars are. Nobody knows who are the most successful, influential, or who has the most power in this new space. For some sectors, take 3D printing, we're still unsure.
The opportunity for community professionals is to use your influence to build stars. Identify the people creating the new resources, writing the best new material, running the top companies or events in this space, and regularly feature their work in the community.
These might be individuals from within your own community or those in the broader sector. Stars provide useful sources of content, expertise, and waypoints for others. You might find stars from within your own organization.
In a short amount of time, you create a social order. You create the people others look up to. People come coming to your community to see what the stars (the upper echelons of their own peer group) are doing. Gradually you identify new people and begin building their reputations too.