The stuff ZD and Intercom (and SFDC) are awful at, where there are opportunities for something else to swoop in: even partial Markdown support for incoming messages, integrations with third-party docs/KB sources, live queue dashboards/visualizations, toggling features based on different support plans, and facilitating handoffs for follow-the-sun support (multiple queues, defined regions/hours per queue, auto-reassigning active tickets across agents and queues, cleaner or richer ticket summarization options).
The ability to define different capacities for the same agent across different queues and how to aggregate that is also an advanced feature which is useful. E.g. I can take 3 in English or one in French and one in English. Or I can take 4 tier one tickets or 2 tier two tickets. Or I can do x tickets for customers on basic support but if I'm on with a customer who has priority... Etc
Queueing and assignment logic gets tricky because requirements can be vastly different across organisations. Hence why there are companies at the high end charging enterprise money.