The War Games simulation works off of your character being in the real world and the enemies and scenarios being simulated. This prevents us from playing as Flood or Promethean characters. What if in certain game types we get to play as the simulation instead of against it. This would allow us to have a unique multiplayer experience depending on the simulated character. Promethean soldiers could have a teleport ability similar to the hologram AA but two seconds after marking the position you teleport there. A cool down would prevent you from panic-porting after getting shot. They would also get an orange HUD.
For the Elites, rather than give them the hyper mobility of Spartans they can have the evade ability, a slightly higher melee, health (not shields) and a higher jump height. They would have their cool green HUD too.
The Elites armour options could be minimal like in Reach and could be given by rank. The soldier armour could be used as a legendary campaign award (The soldier commander armour)
NOTE:
The Elites don’t need this loophole as the War Games simulation only simulates enemies and conditions. The Swords of Sanghelios just need to be present on the War Games deck to take part.
Aaanyway, comment what you think of my suggestion below. I think this would help appease fans in a lore friendly loop hole and it would allow 343 to something new other than just have Spartans only again.
If it gets into arena it defeats the purpose of equal starts if players differ in abilities and weapons. Kind of the reason why we all start out with the same weapons from the start and then you change weapons and such after.
“if” this were to happen it’d need to be in modes where it’s strictly promeatheans vs promeatheans, elites vs elites, and at the least non ranked play.
as sniper said: lore really has no place in multiplayer, it can cause to many issues if done incorrectly(which I think halo already does). If a game is going to use lore to build itself, it needs to be from the start, halo and bungie never built their games off it(they had lore, but it was never a focal point)and 343 is what started it after there was already a foundation in place, the addition of lore into gameplay is part of what causes the rift between sprint, abilities, and other gameplay choices.
Lore isn’t actually a reason why some of the ideas you listed (like playable Prometheans) don’t exist, but rather the opposite. The lore reasoning is created after decisions are made. Your idea would probably be a lore reason for why you can play as the flood or Promethean if 343i would want to, but they are more focused on Spartan game play due to resources, time, or balance, not because of story.