Google's cars are not iPhone 1. They still just have a few dozen or a few hundred, who knows, and they have only been driving 2 million miles until now. They are not even for sale and will not be any time soon. Oor ever, if they don't market their own electric cars very soon or hook up with a car manufacturer.
Tesla can collect data from 5 billion miles of driving already one year after the Giga Factory is full operation, if production reaches the planned 500,000 in 2018 and each car drives 10,000 miles annually. And then the miles accumulate exponentially.
Here is my guess:
After a few million miles of shadow driving, i.e. a few weeks after the first few thousand new Teslas have been sold, Tesla is likely ready for the real thing under perfect driving conditions like those Google experiences in California. So Tesla is going to open for the self driving capabilities in such geographic areas during the day when weather is nice.
After a few hundred million miles of shadow driving, i.e. within half a year or so when Tesla has marketed 1-200,000 cars that have driven for a couple of months, Tesla will have collected enough data to drive in more difficult traffic conditions, like other American urban areas.
After a billion miles, around a year after Tesla has gotten the Giga Factory up in full speed and the first 2-300,000 cars have been on the streets for half a year, Tesla is probably ready for certain bad weather conditions, like rain, light snow, light fog, and for driving in the dark.
Give it another few billion miles, so still before 2020, and the streets of Istanbul or the snowy roads of Nebraska have been tamed.
