See, the Autopilot that came with HW2 doesn't have access to a bunch of features that the older version of the technology already has. Those features include upgraded autosteer, smart summon, auto lane change, autopark, lane departure warning, collision warning and avoidance, emergency braking and cruise control, among others. The company said it needed to "further calibrate the system using millions of miles of real-world driving to ensure significant improvements to safety and convenience" before activating them on the new hardware.
Based on Musks' tweets, it sounds like their real-world testing is going well. Take note that even if Tesla starts rolling out the upgrade next week, you'll have to wait for months to get all the features. The automaker is planning incremental monthly feature releases throughout 2017.