Yes, this is now implemented in svn trunk so it will be in the next release. There is a new Web.config setting:

<add key="UseRelatedSiteMode" value="false" />

set it to true and all sites use the same users and roles as site with SiteID 1, if for some reason your root site has a different siteid, its also configurable.

<add key="RelatedSiteID" value="1" />

I think it needs one more thing that I will try to work on in the next few days, that is, in this mode we can set which roles can edit pages, but there is no setting for who can create root level pages in the site. If I add a site setting for this, then any pages created below root level will by default inherit the same permissions. So it will be possible for example to give a department its own site, create a role corresponding to the department admins and then assign that role as the site edit roles. Its still possible for system admins or content admins to create pages with different permissions. Admins and Content Admins role really becomes that for the whole system of all sites. We may not want department admins to have that power, so this new site edit roles will give us ability to delegate at the site level without sharing the super user roles.

For the moment I've shifted gears and working on a 301 redirect system for pages whose urls change when the page is renamed. After I complete this and the new site edit roles setting, I will make another release.

Best,

Joe