Shared dashboard with everyone

The only way I can tell would be to set the dashboard as a default but that would of course be everyone's default which you might not want.  For our environment our SSO is set by provisioning, and we have three security groups that all users have to be in for access to the site.  You might be able to share it with the group or groups if you have it set like we do and then anyone that is added via AD would have access to the dashboard.  I don't see a blanket "Share with everyone" like I had in ServiceNow.  

Dashboards are only accessable by licensed Service Agent Users. Besides the native Share option in the Dashboard drop-down, there is no other method of sharing. 

What I've seen and done in the past is to cast the Dashboard to external monitors throughout the building. This would be done using the account of a licensed agent, and having them signed in and leaving the Dashboard page open in a browser.