Well... lots of varied opinions in this thread. Clearly, range is still a big issue and there are two primary reasons why range is a big issue. Speed of charging and lack of charging infrastructure.
Some baseline first...
A 2017 Audi Q7 has a 26 gallon fuel tank and combined MPG rating of 21. That's a 540 mile range. And it can be refueled at the roughly 168,000 gas stations in the U.S. in about 5 minutes, or 6,500 miles per hour.
A Model X 100D has a 295 miles EPA range. 80% of that is 236 miles, which takes 52 minutes, or 272 miles per hour. Cadence is then roughly 3.5 hours of driving, 50 minutes of charging assuming one hits EPA rated efficiency. Using the Supercharger network, it's more like 2 hours of driving, 30 minutes of charging assuming optimal spacing of the charging points.
Now, both get hit by efficiency losses with weather (cold, hot, wind, etc.), terrain, and weight. But the Model X "feels" it more because it starts at a far more limited range and recharging. In the winter, combined with slower speed, it becomes more like 2.25 hours of driving, and 40-45 minutes of charging.
Now, going to 2170 form factor cells with zero change in cell chemistry nets a very slight increase in specific energy (Wh/kg). That's because while the cells contain more battery material, the outer dimensions of the cells are also correspondingly bigger. The form factor change by itself is more about cost savings than increased capacity. Therefore, the move to 2170 cells alone does not present a significant increase in capacity of the pack. Nor does it charge faster, or have higher discharge capability just based on the form factor change. The pack architecture was recently revised to make the 100 kWh packs in the first place. Therefore, we can't assume any bumps in capacity based on moving to the 2170's on form factor alone, but we can expect a drop in price using Gigafactory production of 2170 cells. Since the cost of of a 100 kWh pack is roughly $19,000 to Tesla, roughly $24,000 to consumers, a big drop in pack production costs.. say, roughly 25% could mean the pack dropping to $15,000 cost to Tesla, and they might pass along a savings of $4,000 to 5,000 to buyers. Or they may chose to just pocket that as increased margin, or re-draw the mix of features it's hard to see it straight up.
But we do expect, from earlier commentary by JB Straubel and Elon Musk that the Model 3 2170 cells will have a revised cell chemistry. There was only one major revision of cell chemistry since the Rev B Model S packs that I know of... the 90 kWh packs with silicon added to the anode. Likely they've been tweaking the chemistry since, but the specific energy has remained roughly the same. That last change increased specific energy of the cells by about 8%. The revised 100 kWh pack architecture also bumped specific energy at the pack level by ~5%.
What can we expect from the new cells? Well, we really don't know. The various battery cell characteristics... cycle life, specific energy, volumetric energy density, power energy density, c-rate charging, c-rate discharging, and cost are all in competition with each other. Make gains in one area often results losses in other areas. Increase the specific energy, given a particular cycle life, typically means lower tolerance for charging c-rate. There are cells, like the ones in the Chevy Volt pack with comparably terrible specific energy, but can tolerate far higher c-rates for the same cycle life. It also therefore has much higher power energy density. Clearly the characteristics are balanced for a PHEV. For Tesla, their packs are all optimized for cost and specific energy at the expense of the rest. That's ok because of the tremendous size of the packs and the amount of space available in the chassis devoted to the battery.
As a result, with newer cell chemistries, Tesla might be able to choose to a different mix of characteristics. Say, choosing a cell chemistry that tolerates higher charging c-rates as opposed to increasing specific energy. Let's say that Tesla chooses a cell chemistry that can tolerate 1.5C for extended periods of time. We haven't seen that rate with the newer Si in the anode cell chemistries from Tesla/Panasonic. That's charging at ~140 kW average (400 amps at voltage range of 340 to 370 volts). The Model X 100D right now only charges at 0.95 C for the first 80% with a peak of 1.17C. It would cut the charging time down to 35 minutes for 80%, or achieve 400 mph charging. The typical Supercharger use case would then be 2 hours of driving, 20 minutes of charging. For some people, this is the right choice when combined with additional charging infrastructure. On the other hand, increasing specific energy by another 8% would mean a 106 kWh pack, probably marketed as a 110. The actual increase would be 98 kWh to 106 kWh. Assuming nothing else changes, that's an additional 8% in capacity which directly corresponds to range, which then increases to 318 miles.
Of course, a blend is possible. Increase charging c-rate somewhat, increase specific energy somewhat while lowering cost. Of course, pushing one characteristic impacts the others, so one has to choose the balance. We're looking at either an increase of 23 miles of range, or dropping the typical Supercharging best case time from 30 minutes to under 20 minutes, or winter charging from 40-45 minutes to 25 to 30 minutes.
Over time, likely increase charging c-rates is more important than more specific energy once a certain range is achieved. That's because the charging infrastructure will also get much better. If destination charging was more readily available, there's less pressure on the fast charging networks. And the highest cost overall is putting more battery capacity into the pack, then DC fast charging, then destination charging. The cheapest way to solve the range issues is to have lots more destination charging, but of course that assumes your daily use case is otherwise covered. In fleet terms, adding in 8 kWh per vehicle, for 100,000 vehicles is $128 million dollars in higher cost to Tesla. That's half the entire book price of the existing global Supercharger network as it stands today.
Given Musk's comments, I think their choice for the next step is to increase charging c-rate, drop cost, drop weight, but keep roughly the same pack size. Dropping weight alone will increase range. I'd also like to see higher regenerative braking level... hitting 70 kW and more often, which I think is another way to achieve higher range.
