Almost all official contests on Codeforces are in ICPC format (accepted / wrong answer + penalties) or in their own Codeforces style (overall points — (specific coefficient * time + a number of unsuccessful attempts * 50)) (approximately).
What do you think of the start of the IOI-style ranked rounds? (subtasks). I believe this idea will appeal to scholars (and not only) who are preparing for IOI style competitions.
Not sure about rating though, add to the old one or open a new one especially for IOI contests?. Let us discuss this question in the comments.
They would simply have to be too long, not a lot of people have that time. And writing problems with good subtasks is generally harder than writing problems with none. Not to mention the numerous ties a bad contest would have.