[stretchcat]

Crosswords are grid based word games. A text editor displays text in a grid. It seems like a great fit to me.

[yakubin]

Not necessarily. Acme displays variable-width fonts just fine.

However, Emacs is not just a text editor, so it shouldn't be judged solely as a text editor.

[stretchcat]

Emacs also can display proportional fonts fine. But it's proficiency with fixed-width fonts seems most relevant for crosswords.