As you saw at Flightsim Expo, X-Plane 11.30 offers a wide range of new features for airplane authors, who wish to make their airplane engines and systems more realistic. This post links to the documents with technical details that are of interest to aircraft authors mostly. End-users are encouraged to try the Cessna 172, King Air C90 and Boeing 737 of X-Plane 11.30 to experience more fidelity in true-to-life autopilot and other system simulation.
X-Plane has two separate oxygen systems, bottled/compressed O2 and chemical oxygen that can be used for both general aviation aircraft and airliners with separate crew and pax oxygen. How to set up the system for you airplane is explained here: https://developer.x-plane.com/article/the-x-plane-oxygen-system/
Anti-Ice and De-Ice Systems
Airplanes can make use of electrical or bleed-air thermal anti-ice systems, inflatable boots de-ice or chemical TKS anti-ice systems, each with their own characteristics: https://developer.x-plane.com/article/the-x-plane-anti-and-de-ice-systems/
Vacuum and gyro systems
Besides engine-driven vacuum pumps, X-Plane can now also simulate venturi-powered vacuum systems as found on vintage aircraft and electrical backup pumps that are sometimes found in slightly better equipped general aviation aircraft. The interaction of all the pumps, manifolds and instruments is explained here: https://developer.x-plane.com/article/vacuum-systems/
The traditional vacuum-driven attitude indicator is now subject to the same limitations as in real life, and can be equipped with a caging or fast erect mechanism to help cope with them: https://developer.x-plane.com/article/vacuum-gyro-limitations-and-caging/
Propeller-driven aircraft can have distinct behavior of the prop governors reaction to engine failure or loss of oil pressure. Depending whether your plane is a single or multi-engine, whether it is driven by piston engines or propeller turbines, and wether the turbines are of the free-rotating or single-spool design, the equipment might be drastically different. X-Plane now features negative torque sensing in addition or instead of auto-feather, overspeed governors and fuel topping governors, to make turboprop aircraft even more true-to-life: https://developer.x-plane.com/article/propeller-feathering-systems/
Turboprop engines now have additional overspeed and fuel-topping governors for free turboprops, and fuel delivery control for fixed shaft turboprops. How to set up fuel delivery control is explained here: https://developer.x-plane.com/article/setting-up-a-fixed-turboprop-engine-governor/
X-Plane now comes with a few pre-configured autopilots for airplane designers to chose from, and offers more flexibility in creating a custom one.
General Aviation Autopilots
X-Plane 11.30 adds support for single- and dual-axis rate-based autopilots, control over the trim servo, and a separate static system for an altitude pre-selector.
Airliner autopilots learn new auto-throttle modes, Control Wheel Steering, have two independent flight directors and up to three channels for auto land. They can optionally even have a directional servo for CAT 3 landing rollout guidance.
Learn more about the X-Plane autopilots here: https://developer.x-plane.com/article/preconfigured-autopilots-and-other-autopilot-changes-in-11-30/
The documentation for tuning the autopilot constants has been clarified and expanded with new sections about the new autopilot functions in 11.30: https://developer.x-plane.com/article/x-plane-autopilot-params/
Finally, have a look at the X-Plane airliner autopilot in action, performing an auto land in a gusting cross wind: