Maybe this is possible? I don't know. If not I am officially suggesting it to Pioneer. I own a Xone:92 mixer. I was looking to buy a couple of CDJ-900's or better to go with but the price is rather high. This controller (much cheaper) is in many ways similar to the CDJ-900/2000NXS2 etc.
The DDJ-1000 can take additional decks and sources as it is sporting a four channel mixer just as well as two laptops. I prefer to use my Xone:92 so when reading about this unit when it was first released I was looking to see if you could utilize the controllers decks with another mixer and bypass the one built in. This is a feature I think should be optional - why not? If I bought this controller anyway I would have an extra mixer sitting around. Also I think the decks should be able to split off mixer itself thus allowing you more flexibility to do this :)
It also needs a USB port and a display so it can be both a stand alone and laptop 'controller' type unit. On first look I was about to buy it but then I found out it was a more controller focused unit.
Sometimes I think Pioneer releases products that do EVERYTHING I want but that one important thing that would give me my cake and allow me to eat it to.
Just my 2 cents.