Many vs One?

I was thinking, now that SoSE2 is finally on it's way. Wouldn't it be cool if the race hunting the Vasari was revealed in this game? Either at launch or as expansion. But to make it truly epic, how about balancing the race to be balanced in 1v3 gameplay? I.e. the extremely powerful race invades known space and all three races have to fight together to survive.

Or if we use the Rebellion factions, 1v6.

But they should have an interesting mechanic to make it different. Would make for fun game in the community where one playes the big baddie.

What mechanisms would be interesting to add into this type of game? Here are a couple I would find interesting and theme accurate (let's call this race X for now):

• Does not extract resources normally but destroys planets. Can use "High extraction/high" destruction or "Low/Low".
  Unproportional desctruction vs extraction. I.e. you double the amount extracted at "high extraction" bur quadrouple the amount destroyed. The figures are an example. But strategically the race can extract resources quickly and destroy a lot on the fringes of it's empire where it may loose ground. Can also choose to balance between short term gains and long term income to adapt play style and make games more interesting.
  
  Thematically, they need to move as they consume worlds. Cannot stay or they would die.
  
  
• In this game type all players begin with more than regular armies. The "known races" begin with more static defense and maybe a starbase each. X begins with an attacking force, not so much static defense.
  NPC races in between the invading race X and the other players.
  Initial steam roll needs to be prevented and some time for initial scouting and setup time for the "know race" players.
  
  Thematically. The known races live here, have their bases here and are setup with some initial defense forces as there are tensions between them. X is here to invade. No homes, bases and the likes initially
  
  
• Player "death" of known races switches them to active governor/admiral mode of another player.
  This is done to prevent the X player to quickly kill off one player and that players becomes a bystander with no activities the rest of the game. Keep it engaging. Mechanically the governor or admiral would be given command of a section of any players fleet/planets and control these. Preferably a side fleet. The "recruiting" player could assign ships or planets or systems for this ally to manage and offload in decision making. Particularly towards end game as there are more units and fleets this could help the other players in their micro management.
  
  Thematically, the survivers of a lost race move to another races home worlds and keep fighting against the invading force.

Any other fun ideas? This was just a quick write up of a fun game mode that would thematically work in this game that I came up with.