From my perspective, Mongo is what we actually want to use, and OpenLDAP is a necessary evil.
LDAP pretty much has to stay around because of Crowd and the applications that use Crowd, e.g. Confluence and JIRA. So unless our situation with Crowd changes, we’ve got to keep copying username, first+last name, email address, and password hash over to LDAP.
To answer your question @r0bby, I don’t think there’s much hope for OAuth/SSO to migrate over to Crowd. Some of our authentication strategies (Discourse and Desk.com) are somewhat proprietary. Crowd isn’t a core product of Atlassian’s and I don’t expect much development on it from them: it exists to enable single sign-on for their applications, and nothing else.
So I agree that Talk has supplanted the “social user profile” ideas we had for the Dashboard at one point. The need is for OpenMRS ID to support as many authentication strategies as possible. Keeping Mongo around allows us flexibility in the future—we aren’t restricted by limitations to the LDAP model.