Completely agree, chas (there, you never expected that
)...
There will NEVER be a complete replacement for a real piano. But, just like all the other sounds in our keyboards, we hope to get gradually better and better pianos. It will remain a never ending quest, but each generation of technology improves them, to greater or lesser extent. The GrandX is definitely the first piano patch in an arranger that I will sit down and play in preference to my K2500 (w/Piano daughter-card), although there are a couple of sample sets that give it a run for it's money.
If you have a nice 88 controller, and a decent computer and low latency soundcard, I would definitely recommend Ivory. One of the most expressive streaming sets, good phase detail and all the bells and whistles about damper resonance, pedal up samples, etc., etc.. But you'll need a reasonably modern system to use it well.
Then you have the issue of no arrangers with high quality 88 note hammer action keyboards (MS and the 'home' units excepted). People bitch bad enough about the weight of the 76-ers! Playing a piano on less than that is also a compromise (although, again of the arrangers, the G70 keybed is, IMO, the best... try one!).
But the bottom line is the psychological impact of sitting down at a fine real piano, and knowing that there is no transpose button, no way to easily edit your performance, no quantizing tools, no mousing the bum notes. You HAVE to get it right... That's a pressure that helps (if you are that kind of player!) bring out the best, most focused performance you can.
As PLAYERS, I agree. There will NEVER be anything that can fool us. But your audience? That's different. Several of the best GIGA sets and Ivory can completely fool even the well trained ear. once recorded. Ivory's demos are amazing. And the bottom line is, who are you trying to fool? Yourself, or your listener. As players, we will ALWAYS know we are sitting at an electronic instrument (unless they lead us blindfold to the keyboard!), and sitting THAT close to a real piano, there are spacial, 3D and tactile clues that will always tell the truth. But if you record it (which, even on a real piano always diminishes the experience), few can tell any difference.
Finally, the 'perfect' piano...? No such thing. Even with real pianos! Each has it's own sound and touch. Perfect for some kinds of music, not so perfect for others. The advantage, as a performer or session player, of the GIGA/Ivory type softwares is the ability to choose a Steinway for one song, a Yamaha for another, a Bosendorfer for another. Few studios give you much choice, if any, about WHICH piano you want on a track. You play what they have, and forget about re-voicing it for each song!
So, I guess it boils down to, who are you playing for?
Yourself...? A real piano every time (I have no room for a grand, but have a nice studio size upright at home, and love playing it). A session...? Probably Ivory, unless the studio's piano is just right for the track. A live audience...? The G70's GrandX is acceptable, especially if you run stereo, and don't have roadies to carry a big 88 around!
Just one man's opinion, YYMV, yada yada yada...