It seems that the goal is to minimize the number of applications into which users view entering their credentials as "normal". The obvious missing piece then is some standardized FOSS project to handle CLI login.

Of course that is also unlikely to go over well since what the centralized providers actually want (which is fundamentally incompatible with user freedoms) is attestation. Arbitrarily blessing a few browser implementations that are extremely difficult to compile on your own is just a roundabout method to approximate that (IMO anyway).

Edit: It seems like a mistake to me to conflate anit-phishing efforts and IdP. Anti-phishing should be via hardware tokens or TOTP or whatever. IdP should be about large corporations managing user accounts or about individuals gaining convenience, including by serving as an adapter so that the latest popular standard can be used without each downstream service needing to adopt it.