The full package you describe isn't on the market yet, but it's close. GPS navigators have been linked to autopilots for years. Newer WAAS technology gives precise altitude info allowing for GPS precision approaches. New systems like the Garmin G1000, just certified within the last couple years, link navigation with flight data, weather data, terrain avoidance, and even engine monitoring. Systems like the one from Chelton Flight Systems incorporate the "Highway in the Sky" technology that literally makes flying child's play. They have let kids with no flight experience try the technology in simulators. They had no trouble with all phases of flight from takeoff through landing. Synthetic vision systems combine GPS position info with 3D terrain data to give you a good representation of what's outside regardless of the weather. They've also tested collision avoidance systems that transmit GPS position data instead of depending on radar. It works very well, with greater precision and coverage. Instead of relying on radar signals that can be blocked by terrain, the new technology uses simple repeaters that can be mounted on mountain tops to give position data even in valleys. The systems can receive position data from other planes, too, for automatic collision avoidance systems.

All of this stuff is either on the market or will be soon. It isn't cheap - that Chelton system costs about $60,000. Mass production would lower the cost, but it still would be pricey.

One thing to always keep in mind is that GPS systems aren't 100% foolproof. They can be jammed. Imagine the havoc that would happen if hundreds of planes dependent on GPS data were in an area being jammed. You always have to consider backup technologies, such as keeping the old VORs working.