One of the biggest bits of functionality I want to get in the next milestone for Publ is private posts. Doing private posts requires some way of determining the identity of the person who is reading the site. There are a lot of mechanisms to choose from. Most of them are largely incompatible with one another, and there isn’t any single mechanism that checks all my boxes. And of course the standards keep on shifting, and keep on getting a new unifying standard that will fix everything.
So, IndieLogin is a really great way to get started with IndieWeb authentication for people who are in the IndieWeb ecosystem. If you have your own website on your own domain name and an account on one of its connected RelMeAuth providers, it covers everything. But not everyone who I want to grant stuff to has their own website, or the ability to set one up. Siloed OAuth is still useful. And being able to log in via email address is also beneficial.