Why?

The project presented here and developed in more aspects is not the reason and the target itself. It was not why I started the journey on this field. It was just a space where it lead me. There were subjects I needed to clarify and solve. As a basis to the real target that I had on my mind at the beginning.
The real target was - to be able to create and perform cover versions of songs I like. Just pop / rock songs like the Beatles and others. But although I got some musical and piano education, this target seemed too unreachable to me. It was why I started this journey and built preconditions to reach the target. Because I realized that to be able to present cover versions of songs, you need to be able to understand the logic of chords structure of songs, you need to be able to use it in practice, but it is still only half of the journey. The second part, and it is especially important for instruments like piano is - you need to tune and fix the final form of the piece you want to play and learn it - more or less exactly. Pure improvisation generally doesn't work, it doesn't lead to qualitatively satisfactory results.
So let's summarize what you need to play (your) cover versions of songs:
-you need to understand chord structure of the song
-you need to tune it into the form when it is musicaly satisfactory
-you need to learn playing it

If this is what they teach in musical schools (besides the other stuff), question is how this is feasible for musical  / piano amateurs.
The item one I mention in the secion 'The language of music' on this website. Well, I take it a bit from the opposite side, analysing existing classical pieces, not using for improvising on pop or folk songs. But the principle is indicated there.
The item three is described and presented very detaily in the main part of this website.
And the item two - that is the resting part. It is where educated musicians use notation. But for average people using notation is not easy nor comfortable. Especially for tuning the final form of a piece. But I think, it is where software can help a lot. I have quite a good concept in mind. Will it work? Will I bring it to the stage when it works? It is a question of time, motivation and some other factors. We will see.