There are those who said this day would never come, what a day to say now.
yes, that would be a good idea.
i hoped that a thing like that would be implemented in halo ODST.
but my idea is to have the person choose their own race and the enemy's, for example-
-Covenant origional(all the H:CE dudes)
-Covenant (all baddies)
-Humans
-Flood
-Forunners? (sentinels and those big flying things etc.)
it also would be nice to choose to fight or be one race only:
only grunts or infection forms
but i doubt that that will happen :P