I have created a mod which turns commanders into factions or races (for example, Fenix into the Purifier faction, Artanis into the Khalai faction and Kerrigan into the Swarm faction, to name a few).
It is entitled Faction Wars COOP and available in the Americas region. Simply create a map in the melee custom, then create with mod and search for Faction Wars COOP and upon starting, there will be a 20 second timer for you to select one of the 12 factions, and after selecting your chosen faction, you are good to go.
This mod also features 1v1, 2v2 and up to 4v4 PvP (Player vs Player) faction battles, something which is lacking with the current Co-Op mode, and a further hostile zombies or hybrid challenge for a more challenging quest is also available.
Do give this mod a try and let me know your opinion or feedback.
The link below shows the Purifier faction in action against an AI: