I don't think MS is going to take the foot off the COD gas, per se (though, as I've said before, I think maybe a 4 or 5 year cycle with either a gap year or regular "smaller" games to fill the lulls would probably be better than the current 3 year cycle.) But, I do think it's interesting to think about Sledgehammer here specifically. Sledgehammer has not had great press and results lately. In fact, its entire history has been marked by gambles and saves and compromises. Advanced Warfare, WW2, Cold War - where they disagreed with Raven, ostensibly always the support studio, and lost getting relegated to partner studio alongside Raven. Decent/good games that nevertheless did not set the high water marks for their franchise. They've lost both of their founders.
And yet, they've continued to grow - exponentially even. New studios in new locations and a LOT of new people. And they're now working on multiple projects. Here's the thing. Will they continue on the COD train? Maybe, entirely plausible, quite probable. But that doesn't mean their COD project has to look like the yearly COD products we've been getting either. At least one of them could well be a genre and tone or even franchise departure.
In that case, IF The Initiative can prove itself as the "lead" studio on Perfect Dark, perhaps there is indeed a case for taking some of the talent at Sledgehammer, potentially with less direction after high profile project setbacks and the loss of their former leaders, to allow TI to step in and direct them towards something new. It's plausible, at least.