not really sure they should be banned from mid season, double diffusers, despite being against the spirit of the regs weren't banned mid season and neither was the "f" duct.
2012 regs seem pretty clear cut, teams can hardly complain about having to remap their engines for the longer exhausts when they've spent so much time remapping to hot blow the diffusers.
apart from the hot blower issue, i wonder if heidfeld's fire and perez's crash have forced the issue, big side on crash in the renault and you could conceivably get the driver trapped with part of the hot exhaust forced up and over into the cockpit.