Subscript and superscript Unicode in SWI-Prolog

I am pushing a little bit the limits of Unicode support
in SWI-Prolog. Especially parsing and unparsing Prolog terms.
With version 9.3.2 I get the following result:

?- X = π(x).
X = π(x).

?- X = π₂(x).
ERROR: Syntax error: Operator expected
ERROR: ** here **
ERROR: π₂(x) . 

On the other hand, using the JDK 21 Unicode database,
their category definitions I get in my Prolog systems:

?- X = π(x).
X = π(x).

?- X = π₂(x).
X = π₂(x).

I started using the subscript and superscript feature of
Unicode for some proof display. I guess it gets parsed and
unparse as expected in my system because:

?- char_code('₂', C), code_type(C, T).
T = 11

And OTHER_NUMBER = 11 also known as No, I do
allow these in a Prolog identifiers.

Edit 10.06.2024
Not sure whether the ISO core standard meanwhile defines
something concerning Unicode and Prolog identifiers, its my
independet grass root approach, which even doesn’t have

a document specification, only a code specification in Novacore:

sys_type_class(11, is_ident).

These subscripts and superscripst have the advantage that
one doesn’t need some markup, i.e. HTML or LaTeX, and
all that is need is Unicode to have them in documents.

Super cute, i.e. π₁ and π₂, for Proof object constants:


Ok, interesting!

Scryer Prolog allows OTHER_NUMBER in Prolog identifiers:

$ target/release/scryer-prolog -v

$ target/release/scryer-prolog
?- X = π(x).
   X = π(x).

?- X = π₂(x).
   X = π₂(x).

What would be an argument against including
OTHER_NUMBER in Prolog identifiers?

Edit 16.06.2024
One argument against OTHER_NUMBER is that one
can fake a period. For example with this OTHER_NUMBER:

⒙ Number Eighteen Full Stop
“⒙” U+2499 Number Eighteen Full Stop Unicode Character

Now the following query works in my system:

?- X = ⒙(Y).
X = ⒙(Y).