Now, BMW's global marketing manager for M cars, Brian Watts, has all-but-confirmed the car's existence, telling The Detroit Bureau that the project is 'under consideration' but hasn't been confirmed.
That sounds to us like marketing-speak for 'yes, it's coming, but we're not ready to tell you about it yet'.
As for the nitty-gritty of the car, while nothing's confirmed there, we expect a power output in the region of 400bhp, with torque of up to 650lb ft.
This heavy torque output could mean that BMW plumps for four-wheel drive, a theory that is backed up by the M550dX moniker spotted in our previous story.
It's also unlikely to be a 'full-on' M car; BMW knows its market and won't risk compromising the perceived purity of the brand, so expect this to be a halfway-house between a full-on M model and an M Sport spec. And M car purists shouldn't worry too much either - the V8 petrol-powered M5 is still on its way...
So, a four-wheel-drive diesel M car, eh? Sacrilege or a step forward? We'll let you decide that one (and we suspect you'll have a lot to say about it)...
Join the PH rating wars with your marks out of 10 for the article (Your ratings will be shown in your profile if you have one!)