As previously reported this motor will go into the next generation W205 C63 AMG which will have a Performance Package option as well as the upcoming Mercedes-Benz AMG GT (formerly SLC). Will top mount turbos make these cars more attractive performance tuning options? Possibly, but the issue is AMG seems intent on including CAMTRONIC. This is essentially the Mercedes answer to BMW's VALVETRONIC which allows variable valve placement. This will likely complicate tuning for the vehicles and make the Mercedes-Benz factory performance option more attractive until tuners figure the motor out.
The video below explains CAMTRONIC and the illustration gives an idea as to how the turbos will be positioned. It seems the M177/M178 will have more in common with the M270/M274 four cylinder (which the M133 2.0 liter four-cylinder in the CLA45 AMG is based on) than the M157 or M278 V8's. With the M177/M178 coming in at 4.0 liters it seems to almost be a doubled M270/M274 design. We will have to wait and hear official info to know for sure.