It would be nice to have an N/A icon to represent "not available" or "not applicable" etc. I based this design on ab-testing

Not a huge fan of this design for not-applicable. I like the idea of adding this icon, but needs to be different where it looks more like N/A.

Might be better to make the letters a little larger. This might be tweaked a little more.
I am opposed to these text-based, language-specific icons in general. And as long as #4392 (word "NULL" with slash to show "not null") remains rejected, I find it only fair and consistent to reject this in favor of a graphical representation.
I agree with that. I can't really see a use-case for this in an application that couldn't be easily done with text.
I forgot about the issues that would arise due to app translation. I think @JapanYoshi is correct. It should simply be a graphical representation not text-based.