I think they should have brute vs brute slayer. since their is hunmen vs humen and elite slayer. although alot of people hated elite slayer it would be cool to still have the option to mix it up a little if you want. it can be four on four all and they call it brute slayer. also the brute get there own special assinations. like say if a brute assinates a humen the brute grabs the spartan the head head and slams it into the floor. also the brutes should have there own types of weapons. like they could use the spikers and love to use gravity hammers as a class just like how elites had energy swords as a class.
also they should add a 3 race invasions which would be like a squad slayer that has the same amount of people as big team. 5 people per team. 3 different races or you can say teams. humens vs elites vs brutes. all of them in one game mode like slayer or like king of the hill where they have to capture hills that could be builds. also this can be something brand new and never was thought of before or at least used in a game.
then when you do invasion it could be the same game modes except you vote to be humens vs brutes or brutes vs elites or humens vs elites. then if you want after you vote you can vote the maps you play on. i think this would be a good addition to the game.