I don't think the difference will be as large as you make it seem. Sony's sensor may be a little better (sure would hope so for 400 bucks on top of the phone) but Lumia 1020 comes with a high performance Carl Ziess 41 megapixel sensor, with image stabilization, low light performance enhancements, unmatched custom software and 6X lossless zoom. 

Just go through this detailed breakdown and let me know if you still think the difference will be as massive as previously stated...if so, we agree to disagree. 

http://anandtech.com/show/7142/some-thoughts-about-the-lumia-1020-camera-system

I think as long as the phone supports NFC it should work

The girl's one has 10x optical Zooooooom. Not sure how lossless digital zoom compares to optical zoom but seems to me 10x optical is significantly better than 6x lossless. I would think the "budget" version (QX10?) would be comparable to the 1020 but the QX100 should be miles ahead of any built in phone camera currently on the market.

OTOH for what I would want a camera for even the Lumia 1020 is more camera than I would ever need. And as kowen says, for the camera geek a they are more likely to want to carry around a proper SLR camera not this phone attachment. So as nifty as these things look I don't see them selling too well. It's a product without an identifiable market form what I see...the semi camera geek? the wannabe camera geek?

probably also a better bokeh and plenty other important stuff like that (if you take photography serious). 

and 41 megapixel on which sensor? the sensor has to be very small and it has still 41 megapixels? that alone can't be good.

but sure, if someone takes photography serious he will also not jump on this now and will use a dedicated cam.

Looks bad ass, looking forward to playing around with it.

I am pretty sure this is targeted at the prosumer market that think point-and-shoot cameras are not good enough (especially in low-light conditions), and that DSLRs are too bulky.

This lets you have the lens of a DSLR with the body of a point-and-shoot (ie your phone). It is definitely an interesting idea.

Those are called system cameras.. Small Body yet high qualty photos and changeable lenses

Almost every manufactor has one of these in their line ups

yeah, this is what i was thinking.  neat as hell but who's the market?

price has been. ill copy past from the article

"The prices are pretty much as expected – the high-end QX100 will cost $500 (the Sony RX100M II which lends its lens and sensor to the QX100 is $750) and the QX10 will cost $250. Both will be available later this month and there will be accessories like a soft carry case and dedicated camera attachments for phones like the Xperia Z (we’ve seen attachments for the Xperia Z1 too)."

http://blog.gsmarena.com/leak-sonys-qx100-and-qx10-lens-style-cameras-will-work-with-android-and-ios-cost-500-and-250-respectively/

I know :)  I was just pointing out the target market for the other posters who were all asking who the target market was.