I agree the cdj-850's do not support quantized loops, and as you say that would be a new feature.
But thats not the problem, its the fact the auto loops aren't good enough, I.E. if the tempo says 126bpm, and I press an 8 beat auto loop, the length of the loop should be exactly the time of 8 beats @ 126bpm, but its not, you can hear the end of the loop isn't seamless or the timings slightly off, one or the other, and therefore it drifts. Obviously its up to the user to press it at the right time, on beat, as there's no quantize.
And I'm not trying to be patronizing or anything, i know you know how a loops works, I'm just trying to explain the problem as clear as possible.
Still, I love my cdj-850's though! I'm not a hater I'd just like to see this fixed =]