This is different because your grandma would have to buy the tokens once and signup once and she will have access not only to the 'wedding photo service' but a large number of other services. It's more like paying a small amount of money to get access to an ecosystem of services. Like how people pay money to buy an iPhone and this gives them access to the Apple App Store and all the apps therein.
There will also be network effects associated with the blockchain price going up with adoption. People who signed up early to the right blockchains will have priority access to certain software ecosystems and exclusive services which are only accessible to the richest among them (for example).
This seems even more like an anti-feature TBH. Imagine not being allowed to use the future equivalent of basic services because you were not "early enough". Sorry grandma, no wedding photos for you because you didn't buy these specific three coins out of the thousands started every month.
I cannot possibly imagine a world where services will choose to only permit authentication via some expensive blockchain such that they deny themselves access to markets outside of the global rich.
And telling my grandma "don't worry, the coins you don't understand will go up in price" is not going to help.
This is the core question: why is signature-based authentication using public keys associated with BTC wallets superior to signature-based authentication using public keys not associated with BTC wallets? As far as I can tell, the only benefit here is that now my identity on my photo sharing service can be linked to my identity on my wine rating service. Why do I want that?
I'm convinced that decentralized communities will eventually corrupt and destroy all centralized services and agencies by manipulating their employees and members... Because they can. People will always find a way to create new problems to make themselves necessary. In these political games, decentralized anonymous communities have the upper hand. Unlike centralized projects, you can't corrupt decentralized projects. What can be corrupted, will be corrupted.
To understand why it's the future, you need to look at the big picture. You're assuming that centralized auth providers are secure and trustworthy. This is not going to be true in the future. Trust in institutions and organizations has been eroding and will continue to erode.
“Services will make more money because blockchains are trendy” isn’t a meaningful difference.
I'd wager that most people don't care about this much, though it is real. Still, this can be achieved with signature-based authentication that doesn't require the tremendous waste of BTC. Just... tell the service your public key and sign a message when you sign up. Your key pair doesn't need to be associated with some distributed system for that to work. This has been around for decades and not exactly caught on.
> It allows you to use the same passphrase for all services without compromising security since your passphrase never needs to leave your own machine; it is never sent over the wire. You just send signatures to different services.
This is true for all signature-based authentication, which does not necessitate a blockchain.
> The cost associated with purchasing tokens needed to initialize an account on the blockchain would serve as a spam prevention mechanism; an alternative to SIM cards which most centralized services rely on today to limit the creation of spam accounts.
This sounds like an anti-feature to me. Especially since it'd be foolish for a service to only support authentication via a blockchain. Imagine telling my grandmother that she needed to buy some btc in order to sign up for the service that hosted my wedding photos.