Additional banlist in Commander open play queues
I believe that it would be massively appealing to introduce a personal banlist for Commander open play queues.
When a game is started, the creator may have the option of specifying individual cards, or maybe a deck comprised with the desired cards. Any player attempting to join the game would have their deck checked against the specified banlist. Conflictions would remove the player from the game with a status explaining the issue.
In paper, it is common for a regular play group to sit down, discuss the official Commander banlist, make adjustments, and then players will build decks everyone agrees matches the discussed adjustments.
For paper games without an established play group, it is still very common for everyone sitting down to highlight potential cards of contention or ill repute before the game starts. If players are uncomfortable with specific cards, they may choose not to play or switch to a different deck or cards may be removed & substituted.
In the current Commander Open Play lobby, almost every game created specifies specific cards the host does not wish to play with. However, too many players join with the offending cards anyway. This creates non-games where players just leave immediately and the game dissolves. Some players do this on purpose. It can take a very long time to finally get a good Open Play game where everyone is meeting to specified requirements. In a digital client, with absolute control over everyones decks, this should not be so difficult. Games should be more customizable.