> Not to mention that most users would not simply think to create an active
> region before pressing 'd'.

This feature is documented.

> It's better, but a) it shifts the buffer text by 1 pixel, which I actually
> find annoying now that I look at the bottom entry that fits in that window,

My bottom line is partially visible in all buffers anyway.

> b) from your side, it should look suboptimal as well, because the cursor is
> basically invisible when it's on the top line (speaking of WYSIWYG).

Maybe just set window-start to the first non-empty line initially,
thus moving the empty line out of screen?

> If you really must have it this way, do we have an example of invisible
> text expanding when cursor moves inside, and then contracting when it's out
> again? Meaning if would look like an empty line you wanted after you press
> 'C-p', but not visible at all otherwise.

Yes, this is possible: