In the end though, what really matters is the not the absolute quality, but the quality relative to your needs. In other words, are the current 4:3/J1-V1 not good enough for what you would like to do with them? According to DxO Mark, up to ISO 400 the sensor of the J1 is nearly as good as a Canon 1ds, the full frame reference most pro landscape/fashion shooters were using 6 or 7 years ago to sell fine art (still on display today). With probably better AF and more accurate exposure. Is that really not good enough for those cases when you intend to use a mirrorless camera?
I think there is a huge challenge here.
The first is psychological - is an expensive camera still required to "get the shot"?
As a professional, if you turn up to a shoot with a model holding a J1/V1, are you going to be taken seriously?
Would you get asked to leave and come back with a real camera
if you had a NEX or similar small camera, despite the merits of its IQ?
The next is for the manufacturers.
If cameras such as the J1, NEX, etc, can provide the IQ of professional cameras from as little as 6 years ago, then how do you justify your client base spending 5 or more times the price of something like a NEX series camera? Interestingly, both the D4 and 1DX come with something that you'll never find on small cameras: built in gigabit networking. And then there's battery life, ease of use whilst rotated 90 degrees, autofocus tracking but the list is getting shorter...
The real danger is for the DSLRs in the sub-$3000 price range, especially those where the autofocus isn't particularly good/reliable and the feature set is rather, well, "basic". Does that remind you of anyone? (Hello Canon!) So then to replace the DSLR with cheaper and equally capable cameras that are smaller just requires overcoming various hurdles in our mind about what a camera needs to be in order to create a worthwhile image.
To this end, if I had the choice of a NEX-7 and A77SLT, I'd go with the NEX-7 because the A77SLT doesn't offer me anything that the NEX-7 doesn't have. If I get right down to it, all that I need is a bunch of "C" locations along with PASM and accurate (100% magnification) review. Accuracy of metering is pointless because I nearly always ETR and that more or less boils down to tweaking things to get the histogram as far to the right as possible without blowing, so to that end, how well the camera gets the white balance or 1/50 vs 1/80 is meaningless to me.