Did Nvidia mention that? Getting MALI to emulate CUDA etc. would be easier than to get their Geforce cores to be power efficient, unless you want something like the GPU used in Nintendo Switch.
Nothing was really disclosed until the deal was approved but yes, the goal was to replace Mali with GeForce.
Regarding Nvidia graphics IP, it scales very well at low power. In fact, the GPU part of NV SoCs were never a problem on the Tegra line. On the contrary.
Finally, a small story about the Switch, Nintendo refused a deal given by Jensen himself of a custom SoC with Pascal, instead of Maxwell, for only $1 more. With Pascal Tiled based rendering, this custom SoC was planed to be much more efficient and much faster. Still Nintendo bean counter execs didn't see the point and they went for the standard old SoC that we all know and complain about. Lost opportunity...