There's a major issue that needs to be discussed. CF problem setters need to understand that maximum people here are green or grey. They give contests mostly for the sake of learning, and not for competing. So why can't you give tasks based on some standard algorithm? I understand this will make the questions easier for experienced contestants, but giving questions on only ad hoc and greedy isn't doing any good either (I am talking about A, B, C). Please take your time to make good problem sets. Or otherwise, I am sure majority of newcomers will shift to something like leetcode, hackerrank, for CPing.

How about introducing a feature that will give the user to select if he wants the round for him to be rated or not, while registering for the contest?

Many times candidates want to participate in a contest, but the fear of losing their rating holds them back from participating (at least from their main account). So I believe such a feature will have a positive impact in the sporting spirit of the candidates.