According to this bug there is now a /run/casper-md5check.json that says whether or not the file check at the beginning succeeds, fails or was skipped (with most likely fsck.mode=skip boot flag). If it fails, it says which files failed.
So this is all good information we should include in our Apport hook for Calamares. Since there are a number of files already included, making this change (inside the calamares packaging) should be very simple, even for someone who doesn't know Apport.
An aside: it doesn't tell us whether or not the entire installation media is in good working order. That said, even if we do have passes, it still means that we could have a bad install (i.e. bad tooling could incorrectly install good data).