I think this will be beneficial for people who are preparing for OIs, whether it is CNOI mode (no realtime judge feedback) or IOI mode. Since partial scoring is really different from the current CF contests.
I think maybe Codeforces IOI Round #x can be held in parallel with the normal Codeforces Rounds.
Apart from that, it would be great to see more kinds of contests. In current CF mode contests, heavy implementation is nearly impossible given the number of problems crammed into a short timespan. While in a 5h-3 tasks IOI contest, setters can put heavy implementations in. There can be even more possibility like answer-submitting problems (you download the inputs, work out the answer in whichever way you like, and submitting the output).