XCOM 2's expansion is going to be bloody massive. We've talked about this already, following its announcement at E3, but that first trailer only scratched the surface of what Firaxis has been working on. They couldn't properly convey that many new systems in a two-minute video, it's jsut not feasible.
Say what you will about Firaxis, the developer of XCOM and Civilization, it doesn't pull any punches when it comes to expansions. This studio has a fantastic history of using them to tackle big, fundamental issues with their games while adding boatloads of new stuff in the process.