Bloomberg provides some analysis over here and points out that Tesla will need to hurry up because the tax breaks won't last forever. The credit is applied to the first 200,000 electric sales for each new electric vehicle manufacturer, so if regular versions of the Model 3 arrive later than expected they may no longer qualify for the tax incentives:
Tesla is on track to reach its 200,000th sale around the middle of 2018.5 If Model 3 deliveries don't start until the end of 2018, and a higher-priced Signature Series soaks up the incentives for 2019, then by the time a "mass-market" buyer gets a shot at a lower-priced Model 3, the incentives could be gone. In that case, a $35,000 Tesla would just be a $35,000 Tesla. In the meantime, however, Chevy has plans to start selling its 200-mile-range Bolt for $30,000 by the end of 2016, which would mean beating Tesla to its goal of an affordable long-range electric car by a significant margin.Note, the image below is of Tesla's Model S because there are no pictures of Model 3 just yet.