So the M8 rear bumper on these prototypes seems strictly identical to the M Sport bumper, with the exception of a rear apron swap allowing for a sportier diffuser. Actually even the regular M Sport apron would probably do as the quad exhaust pipes would conveniently fit into the voids left by the two large rectangular pipes.
In other words, unlike the M8 Gran Coupé which had a specific rear bumper with larger side vents going higher up until the trunk opening line.
Yes, these are still prototypes, but wouldn't they already be testing the final production body parts at this point?