You can follow along on what we're doing:
Also check out other issues in the Kibana repo that reference OLS.
The summary is Object Level Security -- where Kibana Objects which currently exist in .kibana can have extra metadata on them that specify the owner of the object. Changes to roles and users are required, and improvements to the UI that allows setting these things too. Spaces is this idea that objects can exist in an "unspaced" area where anyone can access them, or they can be claimed into a Space, like a domain, and users can be confined to some set of Spaces.
Read through that main issue at the top; lots of info about the Phases involved here and what we're planning to roll out during each.