If you like this sort of thing, perhaps you'll enjoy my SSL/TLS and PKI history where I track a variety of ecosystem events starting with the creation of SSL in 1994: https://www.feistyduck.com/ssl-tls-and-pki-history/

The short lived certificates started making a lot more sense to me when I discovered I could get Let's Encrypt to issue IP address certs. Clearly, in this context of use we need our certificates to die quickly.

You can now make any web server operate with a publicly valid TLS certificate without paying any money, registering a domain, configuring DNS or disclosing any personally identifiable information. It can be entirely automatic and zero configuration. The only additional service required is something like a STUN server so the public IP can be discovered and updated over time.

It's worth noting that while splitting the PKI hierarchies is a good thing, the CABF does provide rules S/MIME (email signing) and Code Signing. Also, "WebPKI" never actually appears in the BR documents from what I can see, nor do they require the use of HTTP (hence why you can use these for SMTP).

There's a huge suggestion in here which would make PKI vastly more respectable: Disallowing root programs (browser operators) from also being CAs. I loudly suggested at the time Google Trust Services should be rejected but the Mozilla rep loudly defended approving a CA from a root program from a company that happens to pay their entire salary.

PKI as it stands is only a few steps from Google just deciding everyone must have a short-lived certificate from Google to be on the web.

I feel this is a perfect complement to the current 1. link: https://satproto.org/ which implements its own CA system with different trade-offs.