As of 2019, Splunk Connected Experiences is available. https://www.splunk.com/en_us/resources/videos/splunk-connected-experiences.html Part of that suite is Splunk TV which presently allows you to use an app on an Apple TV streaming device (https://www.apple.com/tv/) to view Splunk dashboards and setup slideshows.
At a high level, you have to install Splunk Cloud Gateway https://splunkbase.splunk.com/app/4250 on to your search head or search cluster, enable the Splunk TV feature, and select which apps are visible.
You then have to install Splunk TV on your Apple TV Device, get a device registration code, and register it in the Splunk Cloud Gateway app on your search head.
Once connected, you can choose which dashboards to group together into a slideshow from the Splunk TV App on your Splunk TV.
Most dashboards are compatible, and it even has a nifty feature of auto-scrolling through larger dashboards,
embedded reports are not the same as dashboard. OP wanted a way to display a DASHBOARD without login. Embedded reports are just that, reports, you can not display live real time data. SO, how do you display a dashboard without having to login?