Hi again, Kristinaolga.
I understand your interest in the 'sound' of period instruments. Although I appreciate the full and rich sound of our present-day pianos, I do think it's very interesting to hear the sound of a piano that, for example, Chopin may have played. One is hearing the sound of that piano (the music) the very same way that Chopin heard it, which I think is very neat!!
On the other side of the coin - I once heard a man play a concert on a clavichord, and I was astonished at the sound; how quiet that instrument is and couldn't help thinking that composers in that era would be shocked by the loudness of modern-day pianos. I also wonder if 'our' piano will be altered yet again in the future. Will people 150 years from now say that our pianos sound primitive?
The piano is already being altered again in the present. They are called "digital pianos". Though they have not made it into the "art music" world to any degree, who is to say that they will not in the future. The piano is one of the most difficult instruments to synthesize, but manufacturers are improving them at an extremely rapid pace.
Imagine that in the future a performer could perform a piano recital with his Bach on a harpsichord (with a period tuning and temperment), Mozart on a Stein, Beethoven on a Broadwood, and Chopin on a Pleyel with only one instrument on stage. And the venues can be larger and larger, not needing to deal with the issues of miking an acoustic instrument. Also, since these instruments are more easily transported, the performer is able to travel with his/her instruments and not need to rely on the instruments at hand.
Following this, someone will then rediscover an antique acoustic piano and start a whole new craze for HIP performance on such instruments. Of course the first acoustic discovery will be of an old spinet and the musicologist of the future will create whole erroneous systems of performance based on how the spinet must have been our ideal.....