Ability to plug the CMS data store into Oracle, SQL Server, Informix, DB2, including having different servers for the published web site and the content management system used by the editors.

Connectors to SAP, Dynamics, Commerce solutions.

Connectors to multi-channel campaigns and built-in analytics.

Ability to define workflows, either through rules, or via specific actions.

Plugin based interface to customize the CMS behaviour at all levels, handling the HTTP request, exposing WebAPIs, authentication into various kind of security systems, extending the menu options available on the UI designer.

I guess there are JavaScript libraries to some of these features, however an enterprise CMS brings all of these in one box.

Ah, and a enterprise CMS also has their own set of certifications, developer conferences and partnerships with different kinds of support levels.

What plug-on/integrations do they support?

For example, there are salesforce integrations, as well as the apostrophe-passport and apostrophe-saml modules which leverage passport to achieve compatibility with most single sign-on solutions.