It seems reasonable for server-to-server auth though? Suppose my server xmpp.foo.com already trusts the other server xmpp.bar.com. Now I get some random incoming connection. How would I verify that this connection indeed originates from xmpp.bar.com? LE-assigned client certs sound like a good solution to that problem.
Which is almost exactly why WebPKI doesn't want to support such use-cases. Just this EKU change alone demonstrates how it can hinder WebPKI changes.
> It seems reasonable for server-to-server auth though? Suppose my server xmpp.foo.com already trusts the other server xmpp.bar.com.
If you already trust xmpp.foo.com, then you probably shouldn't be using PKI, as PKI is a complex system to solve the problem where you don't have preexisting trust. (I suppose maybe PKI could be used to help with rolling over certs)