We are just weeks away from starting production roll out.
Please see this:
3,761 votesworking on it · AdminSharePoint UserVoice Admin (SharePoint UserVoice Admin, Microsoft SharePoint) responded
Thanks for your feedback! Just a note to let you know that we’re building your suggestion now. We plan to increase availability to this feature throughout 2019.
Corporate lifecycle is a real and constant pressure in business, often resulting in a need to rename the Office 365 Tenant. To that end we are working on the solution to change the SharePoint domain URL (contoso.sharepoint.com renamed to fabrikam.sharepoint.com). This capability will also then enable the renaming of an individual site collection (contoso.sharepoint.com/sites/abc to contoso.sharepoint.com/sites/xyz).
While we don’t have an estimated delivery date to share at this time, we’ll update your suggestion with details as they become available.
I give this a timeline for at least 2020