Having just run the numbers with a few different scenarios, I think GM will likely cross the tax credit line within 1 or 2 quarters of Tesla.
Also, since it will be hard for GM to raise production of the Bolt to much more than 50,000 a year, it is very likely that about 3x the number of Model 3's have some sort of a tax credit versus the Bolt.
Here is one likely scenario:
Tesla sells 102,500 S+X+Roadster in the U.S. by the end of 2016.
Tesla then sell another 37,400 S+X in the U.S. in 2017.
Tesla sells 60,000 Model 3's in 2017. Any additional production goes overseas or to Canada.
Tesla crosses 200,000 on January 2, 2018.
Production at that point is 50,000 a quarter for the Model 3 alone, increasing to 125,000 per quarter in Q4, 2018 for a total production of 350,000 in 2018. 40% is in the U.S.
For Model 3 tax credits then, we're looking at:
Q3 + Q4, 2017: 60,000 (full tax credit)
Q1, 2018: 20,000 (full tax credit)
Q2, 2018: 30,000 (full tax credit)
Q3, 2018: 40,000 (50% tax credit)
Q4, 2018: 50,000 (50% tax credit)
Q1, 2019: 60,000 (25% tax credit)
Q2, 2019: 70,000 (25% tax credit)
So about 110,000 get the full tax credit, another 90,000 with 50% tax credit, and 130,000 with 25% tax credit, for a total of 330,000 with some federal tax credit.
Note that Musk had actually estimated 100,000 to 200,000 Model 3's in 2017. The above scenario assumes a much smaller reality.
Let's look at the GM scenario. GM has about 120,000 tax credits used at the end of 2016, extrapolating the final 4 months as the same as the first 8 months. Assume very generous delivery numbers for the Bolt, and whatever few they ship in 2016 is counted in 2017.
2017: 30,000 Bolts, total of 175,000 tax credits used in by end of 2017 (40,000 Bolts made, 10k overseas)
Q1, 2018: 10,000 Bolts and let's make the assumption then that GM doesn't cross the 200,000 line until Q2
We're also linear on the Bolt because GM has the production capacity to build into inventory. Also assume that GM ups the production of the Bolt to 50,000 a year, with 40,000 for the U.S.
Q2, 2018: 10,000 Bolts (full tax credit)
Q3, 2018: 10,000 Bolts (full tax credit)
Q4, 2018: 10,000 Bolts (50% tax credit)
Q1, 2019: 12,000 Bolts (50% tax credit)
Q2, 2019: 12,000 Bolts (25% tax credit)
Q3, 2019: 12,000 Bolts (25% tax credit)
So on the Bolt side, we're looking at 60,000 with the full tax credit, another 22,000 with 50%, and another 24,000 with 25% for a total of 106,000 Bolts getting some tax credit. Getting additional battery cell production online for 2019 production right now is very, very tight. LG Chem doesn't have the capacity for much more Bolt production than this for 2017 through 2019. This scenario also assumes that the demand for the Bolt is robust and GM is supply limited by the battery cell production the entire time.
If Tesla's predictions on Model 3 production are on target, then the number of tax credits for the Model 3 is substantially higher, but the phase out would happen one quarter earlier or Tesla would ship more overseas. With the above scenario, basically everyone in line right now gets a tax credit of some sort. Those joining today likely get 50%, but possibly soon it will drop to 25%.
In any case, it is likely that GM and Ford will see that the tax credit program will need to be overhauled. GM doesn't want other automakers like FCA to have an advantage.