Can we start banning players who open mid in a 5v5?

If everyone on the team agrees to open mid to ff early then there is nothing you can do. If just one person disagrees then yeah you can report it.

Open mid is the equivalent of a pre-20min surrender.

If the game is gone, and you chat with your allies and agree that it's gone and want to move on, that's your choice. Just because Riot doesn't give an official surrender option at that point doesn't mean it shouldn't be permitted.

Heck, I even think a 4-1 open mid vote should be permitted, because a 4-1 surrender vote successfully surrenders. If you won't let them open mid they'll just surrender at the 20min mark anyways. So why waste the extra 5 minutes or whatever?

I do, however, think that an "open mid" statement should need to be made by at least 4 players on that team before the enemy team goes for it. And if those players attempt to defend afterwards they could be reported for unsportsmanlike conduct (i.e. trying to gain an advantage by making their enemy think they gave up).