Excuse me for mistakes but I think its readable.
1. No reason to have this, it'll only lead to abuse of the system and toxicity
2. Yes, in a perfect world, the matchmaking system will find 10 players that have the exact same elo, and yes, if you beat a team that has more average elo you will get more elo from that match.
3. This would be a bitch to do properly. Who would want to get matched to a team losing 0-10 and then take the elo hit when you inevitably lose? It would also not find players a lot of the time since it would look for players with similar elo to the leaver, which would be a tiny pool.
4. kill yourself