I think the great thing about that timeslot is that it's somewhat experimental, so the bar might be kinda low ratings-wise. Not sure what ratings James Corden pulled, but as long as the dropoff from Colbert to Taylor isn't too steep I think CBS will be content.
Plus I imagine it can't be the most expensive show in the world, compared to a late night talk show.
/Am curious to see what happens with Hashtag Wars