The challenge with centralized is that it is a single point of failure. The original post was more focused on "If you get locked out of google, you get locked out of everything". In that vein if promise gets hacked/bought/abandoned/changes it's business model etc.. then you lose all your accounts. The anonymous nature of it is great, but this is something Apple already offers with their sign-in with apple which is already widely supported and with the proxy-email solution you can still be contacted by the sites you're signing up with.
I got interested in IndieAuth because of a project of mine[2], trying to make it really easy for everyone to self-host their facebook/twitter equivalent with direct control over who has access. This runs into the problem with wide adoption where you have a separate credential for each of your friends' blogs. With IndieAuth built into the self-hosted platform, then your own self-hosted site becomes the one credential you can use on all your friends' sites. Self-hosted distributed identity for privacy AND ease-of-use.
[1] https://wordpress.org/plugins/indieauth/ [2] You can find the link in other comments I've made on HN