@Glenn
I agree with you about the music that stays. That was not the point anyway, and the actual music is relatively independent of the actual means, i.e. the instrument.
It may be a weak comparison, but nowadays 99% of all piano music is played on modern pianos. That means that e.g. the original pianos of Mozart's time have been replaced by something else (which is an offense to some purists, but it is done nevertheless). We even play Bach on fortepianos while most of his music was obviously devised on a cembalo / harpsichord.
It is hard to predict a timescale, admittedly. But look what has been achieved by PT in just about 3 years (since v1); the progress is downright impressive.
Of course the sound and detail of the most expensive grand pianos is still unsurpassed, but I maintain the claim that the 'cheap' part of the market will soon break away. That has already happened anyway to a certain extent with those Kawai home digital pianos which are really not comparable to PT. I never liked those, still many people bought them.
I'd say that the difference in a real space, provided we're dealing with top-notch instruments, is somewhat larger. I do not quite see PT there yet. But recording-wise, there are but few examples of which I would say they are sky-high above what can be done with the recent PT version. Maybe I am a bit enthusiastic at the moment. We shall see.
Other than that, there is quite clearly a nostalgic motive in many pianists and concert goers. You know, the 'magic' of a grand piano. Personally, I strongly oppose such sentiment; it has nothing to do with the music.
Unfortunately, it is true that many people are awe-inspired by a shiny grand piano enclosure even if it contains a outdated, crappy digital sound generator. But even that will not stop development of technology like PT. After all, it will be easier to maintain, cheaper, more reliable and more flexible. Put it into a cannibalized old grand and most people won't notice a big difference.
It's the way things go; look at the publishing business and the huge revolution that happened there with the advent of phototypesetting and later DTP.
I go quite a bit off topic here, but even painting has completely transcended to the digital domain with some artists. Have a look at furiae.com and you'll see what I mean. This woman is working entirely on a digital graphic tablet, something unthinkable just 10 years ago. Would you have guessed it's not 'real' painting? (She does paint, it's not photo compositing or something; watch her tutorials if you are sceptical.)
The main point here is this: the essence, i.e. the human 'eye' (or 'ear' in music), aesthetics, taste, craftmanship, remains while the tools change. I sense quite a bit resistance, especially among pianists, towards that obvious road map, but that road will be trodden sooner or later.
We're not dumping piano music, just mechanical dead freight. And that's a good thing since the tools get more affordable.