Sure, and if we're coming up with hypotheticals, here are some which are far more likely:
* A blockchain could increase the fees for service. Wait, that happens on a daily basis and you have no control over it.
* A blockchain user could fall for an attack. Unlike the Google scenario, there's no way to regain control of your account – time to setup a new one and convince everyone you work with to update.
* The site you're actually trying to use could switch to a different blockchain (which is more likely than only offering login with Google or that being canceled).
* The site you're using could check a list of addresses and ban yours because it's suspected to be associated with fraud
This is why I suggested taking off your salesguy hat and thinking about what this is like for normal people. Switching to a system which has mandatory upfront inconvenience and expense needs to have a big win to be worth it for people. If it's all “you'll find something to do with it later” you'll get adoption like GPG did.
In this case, I think the key thing to consider is why people use Gmail. It's not like you can't run your own email server, but most people don't want to be responsible for something that important.
Blockchain "service" isn't needed. It's authentication by private key.
A blockchain can be used to tie additional information to the public key.
> The site you're actually trying to use could switch to a different blockchain (which is more likely than only offering login with Google or that being canceled).
I hope they don't use any blockchain at all.
> Unlike the Google scenario, there's no way to regain control of your account
Recovery mechanisms for private key based identities have been designed and implemented.
> Recovery mechanisms for private key based identities have been designed and implemented.
That is not how blockchain works. Once someone has your private key they can make any transactions that they want, you cannot undo those changes once they are on the blockchain.
* A blockchain could increase the fees for service. Wait, that happens on a daily basis and you have no control over it.
* A blockchain user could fall for an attack. Unlike the Google scenario, there's no way to regain control of your account – time to setup a new one and convince everyone you work with to update.
* The site you're actually trying to use could switch to a different blockchain (which is more likely than only offering login with Google or that being canceled).
* The site you're using could check a list of addresses and ban yours because it's suspected to be associated with fraud
This is why I suggested taking off your salesguy hat and thinking about what this is like for normal people. Switching to a system which has mandatory upfront inconvenience and expense needs to have a big win to be worth it for people. If it's all “you'll find something to do with it later” you'll get adoption like GPG did.
In this case, I think the key thing to consider is why people use Gmail. It's not like you can't run your own email server, but most people don't want to be responsible for something that important.