Two words: edge compute. The major ISPs are in the process of rolling this out in trials, with nationwide rollouts likely to start in 2021. The general idea is that you build some amount of CPU / GPU capacity in the boxes on the poles outside your house. Initial versions likely won't be able to support the full Stadia 4k experience, but it'll be enough to play games like Fortnite or Minecraft.

Considering those last-mile edge devices often cost in the tens of thousands of dollars and use a lot of power, including a few hundred ARM cores isn't a huge cost increase for the benefit it provides.