I participated in this co-host market in my area. I thought it was a good idea, because Air BNB did some vetting of the hosts that were invited to participate in the market. In my city, a local host is a requirement so it was important for remote hosts to identify a co-host. Currently, people interested in being co-hosts will often post on this community center and their post will be removed as against the content policy of the this forum, i.e., no commercial postings.
So if a host is interested in finding a co-host, they can post here. It is now up to the host to vet the person presenting themselves as co-host ready.