I can't see them doing that, because whether a site is using HTTPS is visible to end users, and Google and many others had already spent a lot of time and effor

I can't see them doing that, because whether a site is using HTTPS is visible to end users, and Google and many others had already spent a lot of time and effort getting them to notice and care. By contrast, end users know nothing about certificate lifetimes, so it would be hard to explain this change to them.