I would guess that most buyers of certs are not technically sophisticated enough to know that they should have been looking for a cert with a specific encryptio

I would guess that most buyers of certs are not technically sophisticated enough to know that they should have been looking for a cert with a specific encryption algo, especially if they bought a very long-lived cert x years ago. That said, I'm guessing that most reasonable cert providers will allow reissues. What would be the technical challenges facing offering free wildcard certs? Is it just engineering time, or is there something more fundamental? That seems like it would do much more for web security than pushing for higher minimum encryption standards on certs would...