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.
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.
The increases in image quality on ASPC already seem to be becoming more limated by lens tech to me though, no video camera is going to need anything close to the resolution were talking about either.
My guess is that as tech progresses where going to start moving back towards the situation with film where by lenses become the overriding factor in IQ again with FF and MF having an obvious advanatge simpley because the imaging area is larger. As tech improves the cost of these larger sensors is likely to carry on decreasing aswell bringing them more into reach of more users. With MF espeically a decrease in manifacturing cost could have a very large effect on price(both sensors and lenses) since its currently a very niche market.
Lenses seem to be going the opposite direction to me with m43 generally more expensive than ASPC DSLR's. I'd guess because its more difficult to extract the required resolution from a smaller imaging area in a smaller lens(isnt that alot of the reason behind Leica's prices?). If you have that increasing the costs of smaller sensors with higher resolution and the much faster march of sensor tech decreasing the price of larger formats then the costs of the two are likely to become closer.
Infact I'd argue that the rise of mirrorless itself is less a case of former DSLR users moving to a smaller sensor/body size and more a case of compact users moving up in sensor/body size as tech/price allows them to do so.
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.
If we were talking a FF/MF mirrorless I'm guessing it would be a good deal larger than the NEX bodies which personally I view as a bit of a gimmick with there extreme size cutting(which seems to be creating problems with UWA lenses aswell).
Personally my opinion has always been that the holiday/amature landscape market is a big part of the reason for FF's recent sucess(the 5D mk2 and now the D800). Thats why IMHO resolution has sold so well since you could argue that amatures wanting to make a 30x20 print of a landscape shot have more use for it than many pro's. Size is I'd guess a big factor for alot of these users, they might not want something really tiny but a 500-600g mirrorless FF body would probabley be very welcome, espeically if it saved a few hundred on the price.
My point was that such users are likely to want to use lenses in the wide/normal range most often which are generally going to balance better with a mirrorless system aswell as potentially offering size savings as we've seen woth mirrorless UWA's.
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.
Have the V1 and the J1 shown AF performance on the level of the 1DX or the D4? my guess is that such AF performance on mirrorless is still some years off.
In this market the size savings of mirrorless seem much less important to me aswell, why would a sports tog want something the size of a NEX when he still needs to put a massive tele lens on the end of it?
