I think that's an interesting question to ask even now. With pianoteq, or even any sampled solution..
Let's say for practice, would you rather get a small upright, or a good keyboard controller + vsti, or a good dp? It's hard to say, because a tiny upright will cost more, and also limits practicing to regular hours. With vsti or dp solution, you get half acceptable keybed (sometimes inacceptable), with livable sound that won't tear your ears off. And ultimately, you are practicing, so which will improve your playing more? It's really hard to say.
For technique, you'll always need the real thing, no doubt about it. But to just learn a song, or to develop your understanding of a song (for jazz improv, etc) perhaps the accuracy of the action, sound isn't so important, as it's more of a mental activity. But of course, it'll be better with an acoustic grand, etc... just saying for bare minimum.
For me, I learn faster on an acoustic because the sound keeps me interested, and it always sounds fresh. This is mostly a problem in sampled pianos, but also to a certain degree in physmod.. there's just something about an actual audio phenomenon taking place (in a real acoustic) that is physically different from hearing it from speakers or headphones.
That's not to say improvements can't be made on the piano.. there are companies that are still improving on the structure / technology, all that is cool. Seems the reason manufacturers need to keep to certain traditions is to maintain backward compatibility with many music written for piano.. seems to make sense to me, but I guess there's nothing stopping them from making something very different.
Problem is, if something is different enough, then new techniques need to be developed and taught, new music needs to be written to exploit it, etc. Cool for a new instrument, but seems tough for something as established as a piano. But as Glenn pointed out, it happened with the electric guitar, so why not for piano, right? Actually, it already happened with piano through ep and synths, but anyway..
But it's sort of like cinema and tv. tv didn't replace cinema, it just became its own thing. It's not one thing over the other I think. To say that some day technology will replace acoustics is a misunderstanding. That's what synth builders said in the 70's. They started off modeling acoustic audio phenomenons, and ended up with an instrument of its own.
The beauty of any instrument is in its limitations. It is a set grammar, a set of rules. And you write or speak whatever you want with it. Just as nit picking the faults and inefficiencies of the english language is of little value, searching for ways to improve an engraved set of rules seems counterintuitive, especially because those rules are valuable because they are solidly engraved. When you play basketball, those rules better stay consistent, or the definition of the game fades. So, while I think it is important to ponder the possibilities of an alternate piano, the tradition of piano is best left as it is. We just add new things to it.