You may also realize that the realities behind the yoke of a Cessna is a bit different than an Airbus A320. The prior can barely fly straight without a pilot where the latter is extremely advanced in automated control. The TCAS systems require pilot input CURRENTLY, yes. That doesn't mean that also that couldn't be automated. Actually there is at least one midair crash where the pilot chose to ignore the TCAS avoidance direction and pulled into the wrong way, causing a collision. Despite frequent pilot errors, current systems are designed to rely partly in the pilot, this is clear. Technologically speaking however it is already possible to create a fully autonomous flight as multiple drones already show. Airfields can easily be upgraded to specification anywhere where autonomous flight is required. It's simply a matter of cost.