So far, I cannot see any specific rollout date for the new UI.
I was hoping to find something on my Site's release notes, but... nothing. No hint/message about the new UI on the site that's (unwillingly) been part of the EAP. No message on my other sites.
I need to know when to inform my users and customers about this change.
From the comms and various comments I understand that it's supposed to happen last week of March but don't quote me on that :)
I was affected (and it seems I triggered rollback for affected sites :) ) - I did not participate in the new UI EAP but I am a part of EAP for Live Docs/Pages.
But the UI changes were a part of the Live Pages thing - and the rollout overrode my space settings).
Quick screen grab from todays webinar on the new navigation.