According to [1], the specific energy is ~300 Wh/kg- the best li ion cells are ~275 Wh/kg, but only barely. When the OP article refers to 2-3x capacity improvements (2x on the website), it refers to energy density, or Wh per liter. That's not really considered an important metric except for phones. Unfortunately, the battery has to be over 150 Celcius for the solid electrolyte to work, so don't expect better phone batteries any time soon.
The way this would work is that cars would have a small conventional battery of ~15-30 kWh that could supply acceleration power and preheat the solid state battery. The larger battery would just back it up on long trips. How attractive this is depends 100% on how much power they can crank in the battery, since it isn't that much bigger than a normal battery.
Lots of people think solid state batteries will eventually replace liquid electrolytes, but it's effectively anyone's guess. We've had a lot of trouble finding high-power solid electrolytes for a looong time. The main benefits are safety related right now.
The basic reason is that conventional cathodes are highly oxidizing, so when a liquid electrolyte gets too hot it steals that oxygen and breaks down, causing a runaway reaction. Solid electrolytes and metallic cathodes don't have extra potential energy, so when there's damage to the cell like a short or overtemperature it simply burns itself out. The solid electrolyte is also far more stable and isn't very subject to breakdown from overtemperature or overvoltage.
[1]: https://qz.com/1383884/a-startup-promising-an-all-solid-stat...