If Tesla remains as controlling over the Model 3 as they are over the Model S, you'll see a HECK of a lot more "jailbreaking", reverse engineering, and third party knock-off parts. A big reason Tesla has likely been successful so far controlling so much of the market around the Tesla is the high price: People who have them can afford Tesla's services and will be averse to risking the car with unsupported work, and there aren't all that many of them out there (comparatively) to begin with.

With the Model 3 hitting a much wider consumer market, you'll see a lot more interest in ways to get around Tesla.

I am actually expecting you may also see more lawsuits regarding things like software activation requirements vs. holding the title to the car and such. Tesla treats these cars like they're still Tesla's property, and if anything I'm shocked it hasn't been tested in court more already.

So far there's been one successful attack that involved surfing to a 'bad' webpage on the car's touchscreen browser, followed by a malicious firmware update. Tesla's been closing the known holes, of course.