Alas, in this imperfect world, phone calls from random users are how server admins are notified of cert expiry.
In this "imperfect" world nowadays eveyone try to ship his responsability to someone else.
I'll wait for someone else to respond to your comment.
...where a 10-line cron script would have done the same job, in advance.
And then the cron job (that only needs to work every few years) breaks and you find out about it after the fact when a user complains.
Needs to work every few years for each domain. Unless all your certificates expire at the same time (or you only have a few), this will be triggered a few times per year.
And moreover, your scenario is essentially "worst case: fall back to previous behavior." That's not too bad...