Renault are not only unique in their exhaust location, but also their sidepod cooling set up. Its possible that the two solutions are related.
Teams have to find the most efficient way to vent hot air from within the sidepods. This air has to pass through the radiators and coolers, as it passes from the sidepod inlet to the tail of the coke-bottle shape. In order to keep the car as slim as possible for reduced and drag and better airflow to the diffuser and beam wing, teams adopt different cooling outlet solutions to work with the other aero flow structures around the car. In Renaults case the majority of the outlet area is in three places: a tall narrow outlet above the gearbox and two low and wide vents either side of the gearbox. We can see the gearbox oil cooler within the upper outlet, so some of its volume is used for venting this heat. Reducing its ability to vent air from the sidepods.
Renault appear to have chosen the two low\wide outlets in order to boost airflow to the beam wing. The compromise in doing this, is the airflow over the diffuser. Airflow over diffusers might be considered as unimportant, as its the flow underneath creates the low pressure and hence downforce. But with a restricted diffuser height , the use of directing high energy airflow over the top of the diffuser and its trailing edge gurneys, helps the airflow beneath. Effectively making the diffuser act like its larger than it is. With other teams, they use the exhaust gasses or very narrow sidepods to direct as much high energy flow as possible over the diffuser. In Renaults case, the airflow running along the floor does not flow directly over the top surface of the diffuser, as these wide vents are in the way. Some people have suggested the teams are directing the heated airflow from within the sidepods out of these vents and over the diffuser for greater aerodynamic effect. However the reality is different, the air coming out of these vents will be of low energy, having passed through the various cooler matrices. Thus its effect in aiding the diffuser is much reduced.
So why have Renault thrown away some aero gains in this area? Probably because of the exhaust solution, As the flow under the diffuser is accelerated by the exhaust gasses passing under the floor, the diffuser does not need the effect of airflow blowing over the top. Thus they moved to the sidepod outlets to this area and played better airflow over the beam wing.
So far no other team have gone for low wide cooling outlets, but equally contrary to the rumour mils no teams has adopted front exit exhausts either. It will be interesting if any team follows Renaults solution in either of these areas.