I'd guess the limates of optical technology will prevent things going too far in this direction,
There are some M4/3 lenses that have good IQ. Leica's DG SUMMILUX 25mm F1.4 ASPH is one of them. And Canon
has built high quality lenses, for 2/3" Broadcast Video cameras, for a long time.
the NEX maybe small but its still ulimately using the same sized sensor as crop DSLRs.
That's the point. A NEX 7 (1.5 crop) is much smaller and lighter than a Canon 60D. And the Sony sensor is 24 Mp, not 18 Mp like the Canon.
But time marches on, and I'm sure that the next generation of Canon APS-C sensors will have more IQ than the present Sony sensors. Manufacturers leap-frogging one another is how high tech works -- everyone gets to be the leader for a few weeks.
A high MP FF camera does seem like a good opportunity to take the mirrorless route to me though.
The problem with FF cameras is that they require large/heavy FF lenses
A Leica 25mm f/1.4 M4/3 (2X crop) lens weighs 200 grams and the Canon 50mm f/1.4 weighs 290 grams. Percentage wise the difference between 200 and 290 is very large.
This is also a problem for Canon APS-C cameras because they use FF lenses, except for the EF-S zooms. Even though I'm an APS-C Fanbo,
I can see a future need for M4/3 cameras, if you really want to decrease size and weight even more. Me, I'd be happy with a NEX 7 sized CANON CAMERA
with 14mm f/1.8, 24mm f/1.8 and 85mm f/1.8 primes.
FF DSLR's seem well suited to the jurno/sports/wildlife users given the advanatge in AF performance ...
The Nikon 2.7x crop mirrorless cameras (J1 & V1) have the Phase Detect Auto Focus sensors built into the chip and are said to focus as fast as Nikon's DSLRs
" ...Very DSLR-like in most aspects, including speed and tracking ability ..." & " ...This is the result of phase detect sensors being built into the imaging sensor, coupled with the high frame rate of the sensor ..." http://www.sansmirror.com/cameras/nikon-v1-review.html
Like it or not, "time marches on" into the high-tech future.