I might have stumbled over a huge "gotcha" in SharePoint Online. Currently on the E3 plan.
I have created a site collection from the "Blank Site" template (not wanting a cluttered workspace), and have added about 20 custom content types manually. As it turns out, I would now like to add Managed Metadata columns to some of these content types. I try to add a column, but the Term picker shows the message
"The required feature is not enabled for this column type"
It turns out that this message is displayed because the hidden feature TaxonomyFieldAdded is not activated for site collections created from the Blank Site template. On a standalone SharePoint installation, you would just run "Enable-SPFeature -Id TaxonomyFieldAdded -url (SiteUrl)" in PowerShell. But neither PowerShell nor STSADM are available in SharePoint Online, and the required feature is not accessible from the Site Settings interface.
So on the off chance that I am wrong about this, does anyone know a way to enable this feature in SharePoint online? Or do I end up having to delete this site collection and re-build all my content types manually?