If it follows the usual Yamaha timeline it should be out this Autumn.
It's timeline is beyond anything in the past...I'd be surprised to see another KB in the S series.....before something totally new is introduced if at all in this economy.
What goes up must come down.
George Kaye reported several months ago that he did hear from Yamaha about a replacement, and (please correct me if I'm wrong) that it was going to sound fantastic and be out some time during the summer.
I recall that after the PSR-2000 came out, the PSR-2100 came out the next year, but it was almost identical with less than 20 new styles and less than 20 new voices. Then it took two years for the PSR-3000 to come. So that was essentially a three year gap.