[mlajtos]

Yes, the grid paper is a stepping stone for the line paper. However, it is a tradeoff. With grid cells you can tell what symbol is in it. With symbols on a line, you have do guess a lot. Illustrative example: there is a unicode symbol for "colon equal" – "≔" – if you write it in a cell you can be sure you got it right. If you write it on a line you could mean two distinct symbols – ":=".

The problem you mentioned – that you have to plan ahead – is not true for grid cells. There is a part in the GRAIL system demo where it is shown that you can go quite far with this approach. [0]

But as you mentioned, flexibility of handwriting is in its non-modal interactions. I am currently working on a line-based editing, but it's a bit tricky.

[0]: https://youtu.be/UXcHidWnD2g?t=282