Here is the response I got for anyone else searching:
Thank you for you rinquiry regarding Yamaha product. At this point there hasn't been any mention of a replacement unit. The YSP-4100 has been out for a couple years and historically we replace models every year or two. But with that said there still hasn't been any announcements yet.
The Yamaha Customer Support Team
Take it for what you will... Prompt professional response, quite nice.