IMO the grey next gen seats look
awesome - I think they especially go well with the CF trim and all the tech in the Model S, and give nice contrast and brighten up the interior. Of course everyone's tastes differ, and that's perfectly fine
Photos: Grey Next Gen seats + Carbon Fiber + Black Alcantara + Premium Front Console
I've previously had (and loved) black leather seats for many years, though I always found they got too hot even in our mild climate. Not so now with grey (& with pano roof too). And after 8 months, absolutely no problems with the grey seats getting dirty, YMMV.
If there's a big demand for grey and if perhaps Tesla is having supplier issues, then that might be the delay on new orders? If you're thinking of the grey I don't think you'll regret the choice, assuming you can wait until mid 2017(!)