Pretty much the title.
Are there any other races/species you would want to be able to play as in Matchmaking?
It would increase diversity and competition among players and be overall beneficial to game play, so yes it what i say.
If you agree and would want to play as different races in MM, then which ones?
I myself would like: Spartans (obviously), Elites, Brutes, forerunner manipulars, and maybe some sort of more humanoid promethean.