The cropping argument is often given, but I don't think it is very valid. A crop from 54 to 10MP is a crop factor of 2,32 and the m43 is 2. A m43 at 16MP not cropped would give better IQ. I don't see much point in walking around with a full frame camera unless one uses the full sensor area for taking the pictures.
The cropping advantage is clearly less of an advantage for those who are obsessed with pixel count and resolution, as I am and I suspect you are.
I would certainly prefer to use a 150mm lens with my 54 mp Nikon rather than crop a shot to 10mm. which had been taken using a 50mm lens.
I was addressing the concerns of people who are not particularly obsessed with resolution
, such as John Camp. That is, people who might think that 10mp is quite sufficient for their needs.
It wasn't so long ago that I was very pleased with the performance of my Canon 40D, which is 10mp. Just out of curiosity, I checked the DXOmark test results comparing the Nikon D7100 with the Canon 40D, at the pixel level.
The pixel quality is very similar, except for DR of course. The smaller D7100 pixel wipes the floor with the 40D, regarding DR performance. If I weren't a bit obsessed with resolution, I would definitely prefer a 10mp crop from a Nikon 54 mp full-frame than an uncropped shot of the same contrasty scene taken with the 40D and 150mm lens.
Of course, a good 150mm prime should give at least marginally better resolution on a 40D because the 40D pixels and sensor are a bit larger than the 10mp crop from a 54mp full-frame and therefore make less demands upon the lens.
On the other hand, a fairer comparison would be the 50mm prime versus a 50-150 zoom. Does a 50-150 zoom with a constant aperture of F1.4 exist? I think not. If some manufacturer were to make one, it would be rather heavy. I suspect that such a lens attached to an Olypus 4/3rds, or Canon 40D, would weigh more than a Nikon 54mp full-frame with 50/F1.4 attached.