I saw a demo of it on the European SharePoint Conference in Copenhagen in 2018. Sebastian Fouillade, who showed this, compared this big change with brain surgery. All the urls, all the connections. But now it is possible. Today I have seen it even in my standard release tenant.
It is really appreciated. Soon it will be possible to rename misspelled sites, like “devlepment” to “development” etc.
To rename you need to go the SharePoint Admin, find your site among Active sites and click on “Edit” in the site url area.