It's obviously serious, but I think its very similar to what UEFA had + the not time barred stuff. I suspect much of City's initial defence will be that they've been through much of this already, that if you remove the suspicion that it's read with via the leaked emails that there's simple explanations for much of it, and that they ultimately haven't shared those details with the league because they don't trust them.
My gut feeling is there will be a big fine, particularly on non-compliance, but rival fans wanting titles stripped and us relegated to the conference are setting themselves up for disappointment. Or City really have spent the last decade being almost criminal with their books and sloppy in hiding it.