Matchmaking chat ought to wait for everyone to join before opening.

This is a scenario I've seen far too often:

4 players, including I_main_ADC, join the room I_main_ADC: adc I_main_ADCToo has joined the room I_main_ADCToo: adc I_mainADC: I called adc

Much arguing later, ADCToo ends up playing a champion he or she isn't comfortable with, a champion completely unfitting for his or her role, or outright disconnects from the game or goes afk in the game

This sort of argument annoys me to no end, because people end up getting shut out of the role they want for something that happened before they could tell anyone else they wanted that role, and could never see themselves. Not only does that end up as unfair to that player (just because they happened to connect two seconds after everyone else), this just causes caustic levels of conflict for the entirety of the champion selection, often crippling the team before it even sets foot into the actual game.

Instead, then, I would rather see the matchmaking chat for one's team open only when the entirety of the team has joined. I would rather have everyone on my team know that I want to play support and lose two or three seconds of discussion time than call support, have someone join, have that someone call support, and have a massive fight ensue.