Critics arent always a bad thing might I add... I don't want to get too involved but there is such a thing as "Constructive Criticsim" which can help you.
But If you want my opinion on this thread, I highly doubt that the Flood will be in it. I'am fairly certain that it is situated around the UNSC not the Covenant.
If they make the Covenant a playable race with thier own campaign well all well and good, but I wouldn't get your hopes up, I'd say that this is a Cov. and Human fight.
And if the Flood were to become a playable race (even less likely) it wouldn't be consistent with the rest of the storyline,