the exhausts aren't at the back anymore, they come out of the sidepods like periscopes
he is talking about them making the diffusers more efficient as they are no longer blown by the exhaust. The theme this year is slimline rear ends, similar to what williams did last year with their tiny gearbox.
thinking about it, the exhausts could be used to create downforce but only in full throttle corners, but the cars will have this extra downforce on the straights as well. Is this desirable?