Here's a recent thread from the OpenStack mailing list. The second message describes the theory behind how to do this: http://www.gossamer-threads.com/lists/openstack/dev/34222

Basically, Keystone is an HTTP service, so you can make it distributed and highly available just like any other web site. The key is to make sure that the data that Keystone relies on is configured in a distributed fashion. There's no set way on how to do this, but the OpenStack HA Guide might give you some pointers:

http://docs.openstack.org/high-availability-guide/content/ch-intro.html

The answer is yes and using a distributed file system, such as Ceph, is the way to do it. Canonical's HA reference architecture is a great example as it uses Ceph to store a lot of the Openstack data.

https://wiki.ubuntu.com/ServerTeam/OpenStackHA