This is what IXEG said about TCAS.
TCAS. Omitted due to time constraints, definitely planning to add later. This is a VERY complex system, and to get it right (including all the modes, synchronized avoiding behaviour of both TCAS systems involved in the conflict, multiplayer aircraft, correct EADI display) will take a long time. You can hear the basic X-Plane audio warning, but no symbology or resolution advisory for now. The system is also very rarely used in real flight (fortunately), so the return on investment (development time) is very low.
And gravity landing gear extension handles are modelled.