SharePoint Hub Sites allows you to associate multiple team sites & communication sites together to bring it in a single view. Hub sites can also aggregate content from the its associated sites like aggregating news/events.
Microsoft has released an official message about the release of Hub sites in SharePoint online/O365 on March 8, 2018. We can see hub sites rolled out starting late March & complete by mid-May.
After a hub site is created using a template type, admin-approved site owners can associate existing team sites and communication sites to the hub site. One good news is you can convert your existing modern team or communication site to a Hub site by running a powershelgl command. The command looks something like
Register -SPOHubSites https://tenant.sharepoint.com/sites/Communications
The documentation for the command is yet to be made available by Microsoft.
This is a new feature release and hence this will not affect any of your existing implementations.