I’ve been looking at running a POC for one of my clients and had the need to create a content type hub for the environment. After looking through the admin section and finding nothing, and then doing a bit of research I cam across a link in the site settings of each site collection:
Content type publishing
So in a word, the content type hub is already provisioned for you in your SharePoint online tenant.
Clicking on this link will show you that your content type hub sites at /sites/ContentTypeHub/
Assuming you have sufficient permissions you will be able to create your content types and publish them from this location. I will post details of creating content types in a content hub in a later blog.