I genuinely am not understanding why you think WEI would make this easier. You have one central place that you log in to set up this payment system, I guess Google in this case, and then other sites check with the central authority to see if you're a paying user. They can use this attestation or a cookie or a Log In With Google button, what's the difference? Either way when you browse from a new device you'll have to log into the payment system again.