Probably will get ignored again, wouldn't be surprised though.

Please, just stop with the challenges. They may be good, it just gets repetitive.

1st Proposal: Zombie Infection Mode

in this gamemode, the player can be randomly selected as either a zombie, or just a normal player, (zombies make up 25% of the lobby, which is a max of 20-30, (preferably 20)).
The players are given a limited amount of upgrades and must survive by any means necessary for the full time limit. The players get one life, whilst the zombies get an endless amount. When a player becomes a zombie, they will have to choose between melee, or ranged.
Other Additions: Secondary skin option.
This mode would basically be a customization overhaul, adding a large number of zombie-based skins. This secondary skin option would have an option that allows it's used as a primary skin in other modes. By default, this skin would be a zombie variant of the player's currently equipped skin.

2nd Proposal: Team-based capture the flag mode

In this gamemode, a lobby of 40 players would be divided in half to fight against each other. A new destructible item will be added. this would be called something along the line of the name Revival Anchor, as it lets the players respawn after being killed. If this item is destroyed, the enemy team's members will no longer respawn. In private servers, players can choose the team they want to join.
Benefits: FANTASTIC FOR CLAN WARS (I don't know if those still happen).

Best of all, both could be added. and each would have the ability of having custom workshop maps!