A PSR3000 would be a cool idea (especially if it kept all of the keyboard's controls in the same layout.
However, realistically speaking, it is not likely to happen. There is little competition in the module market - the only up to date offering is from GEM, and from Ketron (more or less), and Ketron seems intent on alienating its user base by not dropping level of customer support. There is simply no impetus on Yamaha to build a high-end module (and besides, it was never their thing - there was never a high-end Yamaha module).
In addition, the price of the PSR3000 is lower than a module from either GEM or Ketron, so if you want the functionality, just buy it with the keyboard. Some will say it is not as compact, but so what? You can use the PSR3000 better than a module, especially as a vocalist or a guitar player, or just put it on top of your favorite keyboard controller, or an electric piano.
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Regards,
Alex