Browsers could add the less severe warning before the certificate expires, for example 3 days before it expires have a "this certificate is about to expire, are you sure you want to continue?" warning. That would maintain the security guarantees around expiration while still getting the attention of users/administrators.
Isn’t that what happens now when the cert expires? Except when it’s expired it’s a lot harder for users to figure out how to bypass the warnings so they can visit the site to find a contact link to report the issue.
Remember not every site is actively checked by their maintainer every day.
In an ideal world it shouldn’t be needed (and likewise UX for expired certs wouldn’t be needed), but in practice I think it has merit.
