I think there's a few things that have happened.
First, you have to realize that DJ tech is in relative terms, very young. Just look at the first dedicated (not repurposed live desks or broadcast stuff) around in the 80's and they were so basic. The crossfader was a massive revelation and that was around 1984. Then we got EQ's and Pans and then kill switches, then outboard FX units. These were all things that made incredible changes to the very fabric of DJ'ing.
As time went on, even though there were larger changes such as CDJ's and DVS, the basic premise from those first fundamental changes became much lesser increments of change - they've largely been convenience changes (i.e. easier to have more tracks or easier to beatmatch etc) and not really affected the art/craft itself.
It's got the point that "new" kit now is really just bells and whistles and IMO, it reached a critical of critical diminishing returns, where these changes weren't actually adding anything (i.e. pioneer's ever growing list of FX or endless flooding of the market with newer Mk.2 or 3 models which were really BETA product fixes). You then had mixer manufacturers like Innovation doing crazy shit like drum machines built in and transform switches which were moon shot stuff, most of it didn't stick (drum machines) but some did (leds for channel levels, transform buttons etc), and then other brands like Gemini and Numark which made the technology cheaper and more accessible but they didn't really break ground in terms of function.
With the above in mind, we're somewhat plateaued in terms of technology - we have what we need to achieve incredible music and a great DJing experience.
I for instance use a mixer (Vestax PMC 55) that was the pinnacle of engineering for DJ tech at it's peak - it does everything you need and if you need all those bells and whistles, it has the signal flow and I/O to accommodate. The only mixer than has made me interested was the new rane but seeing as I've got a brand new, untouched still boxed PMC55 as a spare, I can't really justify spending $2400+tax on a mixer that has the same functionality but adds a sweep filter.
Pioneer really dug themselves in to a hole by constantly pushing new things that weren't innovative. They also were incredibly bad at listening to people who used their stuff every day like venue engineers and live sound guys and proper working DJ's (not redlining fistpumping jesusposers). They let the marketing dept control their design decision and they paid for it with their company and reputation.
Technics basically nailed it 35 years ago and that design remained unchanged for a good reason as ATX alludes to - when you nail it, don't try to fix what aint broken.
And that's really the state of play. I am interested to see what the new 1200 brings as there seems to be a lot of updated technology to an old design so they may have actually perfect their own mousetrap but time will tell.....
....and even then, it's not like it's going to change the way we mix, is it?
Cue up two records, and mix them, using cuts, fades, EQ and Pan, maybe if your so inclined, sprinkle so fx but unless something changes that fundamental premise, there's won't be any real big new innovations in DJ'ing.