Anything can happen, and it usually does. I think it will be more of a problem when you combine all of the other aspects that have been mentioned, inexperienced drivers, tight circuits and the desire for the best of the rest title since all of the new team will be fiercely competing with each other. Almost two separate races going on. I thing the larger the gap between the leader's pace and the back markers the easier it will be. But if towards the end of the season the gap has been cut to around 2 seconds then it will be a bigger issue.
Actually, the closer the pace is the less of an issue it is.
For safety yes, I'd agree but not for passing.
For passing. Yeah, if one of the established teams has a failure and can't set a time during quali, and has to start last. Sure it'll be easy as anything to overtake those 6 new cars.
But we're talking about the issues during qualifying, with cars getting blocked, and the speed difference causing problems.