To be fair, what Elon described as technologically feasible by the end of the year essentially is level 3(car can handle entire driving task most of the time, but human might need to take over in some situations). Level 4 implies the human can clock out entirely, which he suggested is feasible by the end of 2020.
The way I understand “feature complete” is that AP will pay attention to all needed aspects of driving and that is about it. It will look for traffic signs/lights, line markings, other drivers but with undefined accuracy and likely will not act on many of them. Most features will be in passive mode and car will still require drivers attention and input.