I posted this question in the Yamaha PK Owners forum, and the consensus seemed to be that the Tyros 3 would have the same slightly narrower keys like the Tyros 2 and S900 have.

I had done some tests - measuring a lot of keyboards and pianos ... and only Yamaha's keyboards came in less in key width than most standard keyboards and pianos. I had even gone to some piano stores and measured lots of pianos! Then measured Wersi, Korg, and other keyboards.

I found that the 5 octave span of most keyboards and pianos out there is 33.5" (33-1/2 inches) while the Yamaha Tyros 2 and S900 were 32-1/2" for 5 octaves.
So, there is about a 1-inch difference over 5 octaves between Yamaha arranges and most other keyboards, organs and pianos.

Jim