Do you know in what x-pack release it is planned for reporting to expose a configurable index?
Perhaps this may depend on any multi-tenancy features getting pushed into Kibana itself. The current state of play necessitating different kibana instances per tenant could be improved upon and there are a couple of alternative solutions being offered with search-guard and https://github.com/wtakase/kibana-own-home plugins (i.e. a multi-tenancy solution with a single kibana instance). However, they don't offer any solution by way of reporting.
This stack is really neat, but issues around multi-tenancy are currently an obstacle to adoption. Are there any other options regarding reporting and multi-tenancy other than waiting for it, which may not be a problem if a solution is due to be delivered shortly.