Indeed, of course this would be ideal so that those of us who chose the Grand 3 pianos over others can upgrade at a discounted price rather than have to totally start over and practically crossgrade to some other company.
In my opinion, the competition has really intensified in the piano VSTi market since 2009, with all sorts of high quality options now available. If there was enough demand for a sequel, I could see this happening but read up on how many Steinberg VST instruments have abruptly been discontinued.