Codeforces's virtual contests are probably one of the best feature in CP, since it allows people who can't do the contests because of various reasons to have a chance to simulate the contest. However, the virtual contest format doesn't consider the fact that the real contestants had pretests and system tests, while in a virtual contest, the source gets evaluated to all the tests in the moment of submission.
So, I suggest that the virtual contestant should be able to choose whether he wants to get his solution tested only on pretests(just like in the real contest) or to have full feedback(the current format of VC as of now). I don't think this isn't that hard to implement, CF can probably still evaluate all the tests and show "Pretests passed" if the source passed a certain test number(the number of pretests which this contest had).
I think this is a problem which concerns most of the people who are using the virtual contest feature, so fixing this problem would improve this feature significantly.