It seems you don't really read my post (not the first time IIRC). Please read it again.
Yes I did read your post, and I read it again to double check. I understand it as you meaning that if you type text into a program that you as the programmer wrote, you know what limitations you can apply, because
you know your needs. What I'm saying is, if you develop a Text Editor (or any application that has text input) as a product you want to sell, you as a developer cannot make the assumption that the end-user will never use code points above the BMP. Yet that is what you are doing and suggesting here on the forum. That is what I consider wrong and sloppy.
On the other hand, if you use UTF-8 correctly [1], you automatically support the whole Unicode range.
[1] When I say “correctly”, I mean don't do rubbish like the following. Everybody should know by now that you can't do that for
any Unicode encoding.
var
i: integer;
c: char;
begin
for i := 1 to Length(s)
c := s[i];
end;