I owned a 9000Pro for 3 years and admit it was the best board I have had the pleasure of playing. Can Yamaha make another 76 key board....YES but it's all down to costing. To produce a 76 note Tyros would just not be cost effective for people to want to buy it.
I was told by a manufacture that the major cost of an arranger is the hard ware, a good quality keybed being the major part.