GeForce Now is doing much better.
Stadia had other issues beyond fast Internet, like asking a community focused on Windows/DirectX to add support for the Stadia/Vulkan stack.
At the last Stadia developers conference, a few months before it was killed, one of the talks was about doing something like Proton for Stadia.
EDIT: Here is the talk,
"How to write a Windows emulator from scratch"