The thing is, implementing a CoD style meta-game doesn't even seem to have increased Halo's audience.
The addition of the unlockables/points based metagame was the biggest (non-gameplay) change made with Halo: Reach and it did not manage to attract half the audience Halo 3's multiplayer did, despite a dramatic increase in the install base, despite the metagame.
Why take Halo further in the direction that Reach established was mistaken? What makes CoD popular might not make Halo more popular, not because they have different audiences, but because they are different games. Halo does not lend itself to unlockable weapons or perks... maybe that's why 343's implementation is so half-hearted, why they boast that it doesn't seriously affect gameplay.
It seems that 343 thinks the metagame will make the game more popular. But the best way to make the game more popular is to make it better. The increased emphasis and importance of the metagame will not make Halo better -- it won't make a dent in CoD's population, either.