It's a bit like comparing apples to oranges in my opinion.
First of all :
You can not compare a DSLR sensor to a sensor from a MF camera.
Due to the larger sensor the LOOK of the images is different, already mentioned before the DOF is totally different but also the angle of view. Of course one could choose a 50mm on a DSLR and a 80mm on a MF but still the look is different.
Then we have :
1 fps for MF which is a great tempo to work with for for example fashion, this could be solved by firmware on a DSLR I know, but it isn't yet.
With leaf shutter lenses you can go up to 1/1600 with strobes or higher.
I know that with SOME strobes and Pocketwizard you can get there also using Hypersync but for example in my setup (all A heads on Rangers/Quadras) it simply doesn't go higher than 1/350, I can go higher with a D-lite but those I don't use outside and that's were it counts.
Diffraction, with the 33MP Leaf AptusII I can shoot without any problem on F16-F22, with my 5DMKIII I see a degradation in the image above F11 on some lenses.
But maybe more importantly, when shooting for example fashion MF makes it possible to shoot from the SAME distance with longer lens and higher shutter speed with strobes, meaning we can get shallow DOF while fighting the sun (using strobes on full power).
I really wonder if we had the same conversation if the D800 would have been released with 24MPs. It seems that as soon as people see a camera with the same amount of MPs that MF has the discussion starts up again.
By the way I will not say that the D800 or 5DMKIII is a bad camera, but I base my decision which one to buy/use on the "horses for courses" idea. Meaning with AF nothing beats a DSLR, High ISO DSLR again, recovery from shadow areas seems the D800(E), however when I want to shoot a studio fashion series where I control the light there is no need for lighting up the shadows, but here the 1fps is ideal, the extra shutter speeds with strobes and of course the totally different DOF, meaning for those sessions nothing at the moment beats a MF camera.....
Now fast forward a few years (maybe shorter)
The first REAL mirror less camera is released, no more limitations in shutter speeds with strobes, we get a 24MP foveon type sensor (real 24MP) I think now is the time I will sell my MF gear and forget about the different look, working with one camera for all sounds very tempting, especially because we travel around a lot, and dragging two complete sets can be very cumbersome (and expensive). But I will NEVER make that decision based on MP's alone.
I do wish to add that the D800(e) is a very fine camera, especially the Sony sensor looks very promising, but when I look at 100% crops we shot during a workshop in our studio I do find that fine details in hairs look a bit "chaotic" compared to the razor-sharp MF files, also even with the use of color checkers I can't get the colors in the neighborhood of the Leaf Aptus back, and skin tones are without a doubt the most important thing for me, so even when I would forget all the rest, for skin tones alone I would not think about switching.
But the future looks promising let's hope the technology also drips through to MF camera, I would love to have a system I can use up to ISO6400 (heck even 3200 would be great) with the same quality my 5DMKIII gives me, add some killer AF and I'm more than happy, but up until than I will choose the camera for each assignment, and for studio/strobe work at THE moment nothing beats my MF system.
Now one final thought.
Can I deliver all my commercial work with a DSLR.... ?
No problem at all, it will look different, I can use ND filters to "help" with the strobes outside, 22MP is more than enough for almost any publication.
So why invest in a MF system?
Simply put... because I want the best quality I can get, it's a personal opinion, if you just want to make money get a good pro level DSLR with a 24-75 and 70-200 lens, some good strobes and you can work forever with that, never needing to upgrade, they did with far worse in the 70's and 80's and the magazines haven't gotten bigger
If you however are driven by passion to deliver the absolute best out there and LOVE working the MF way, I think MF is the way to go for now.
In the end it's actually all a bit silly that we look at technique and forget about the thing that really counts.... getting the shot. And me personally I would rather get the shot on the very unprofessional "P" setting with Auto ISO and bracketing than not getting the shot
(not to say that I do, but I think you get the general idea), maybe we are too obsessed by the numbers and forget the essence of photography... getting the shot.