One additional note… there are often contractual limitations with enterprise customers that literally prevent us from discussing those customers and those customizations, from a legal perspective. It’s unfortunate, but what can you do? We have to stay in business and pay the salaries of the folks who work here. That’s something I feel quite strongly about; it’s my obligation to keep things running at Discourse so our team can put food on the table and raise their families with a reliable source of income. 
The good news is that these extensive customizations do slowly trickle down into the open source codebase over time. But it does take time.