Subscript and superscript Unicode in SWI-Prolog

General
1

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: X = 
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.

2

Ok, interesting!

Scryer Prolog allows OTHER_NUMBER in Prolog identifiers:

$ target/release/scryer-prolog -v
v0.9.4-55-gd6ac0355

$ 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?