I am not sure if I should interpret this as "sql-backend is a second class citizen that shouldn't be used in production environments (i.e. think of virtual directories) because of its experimental stage" or take it as an overstatement been made on purpose mostly to discourage new users from considering an sql based engine for their main ldap database backend.

I hadn't had the chance to use sql backend in production or test it as much as I would like, thus it would be interesting to hear from others in the list, their practical experience of sql backend in read-only or read-write deployments.