Our best hope is kicking up a huge fuss so legislators and media will notice, so Google will be under pressure. It won't make them cancel the feature but don't forget to remember that they aren't above anti-trust law. There is a significant chance that some competition authority will step in if the issue doesn't die down. Our job is to make sure it won't be forgotten really quickly.
The whole "this will block bots" part of the spec is complete bollocks and a red herring to distract from the real purpose - to block adblockers and competition from new browsers. And DRM, of course.
If even extensions can be detected, why wouldn't selenium be detected? Granted, I don't know how it works exactly.
In addition to the 5$ robot arm you need to add 200$ for the device it is operating. Drastically raising the cost to run a bot farm is key. You can't fully eliminate inauthentic behavior, but you can make a lot of it unprofitable.