Of course, it will still be very close.
Even once Cadillac started improving the quality of its cars and becoming a far more competent sort of luxury car maker, BMW probably still saw the M3 as being safe from this threat. After all, even the best non-BMW compact sport sedans are still referred to as "M3 killers". The M3 doesn't need that, it sets the bar. But the following video shows an ATS-V (still wearing camo) going doing 0-138-0, and it is pretty damn quick.
Although we can't see the exact number, it seems that it might be quicker than the M3 DCT's 3.9-second 0-60 time. And no matter what, it is certainly a serious addition to the segment.