If you s/Perl_croak/Perl_warner/ in the patches above then you can make it a warning, rather than a fatal. Then you can install a signal handler to deal with it as desired. Nothing should break, although things might get a bit noisy.

Perl_warner( aTHX_ WARN_SYNTAX, "Stringified reference\n" );

/* or you could make references REALLY strict ;-) */
if ( PL_hints & HINT_STRICT_REFS )
    Perl_croak( aTHX_ "Stringification of reference disallowed\n" );
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It looks like it is pretty easy to add a new item to strict as well. *Untested* there appear to be only 3 modifications required. The PL_hints var contains a number of hints set at compile/runtime. The hints are accessed via HINT_ constants set in perl.h There are plenty of spare mask bits. 0x04 is documented as unused so you could

/* in perl.h with the rest of the HINT_ defines */

+ #define HINT_STRICT_STRINGIFY       0x00000004

/* in sv.c as noted by xmath */

+ if ( PL_Hints & HINT_STRICT_STRINGIFY )
+    Perl_croak(aTHX_ "Stringification of reference disallowed");

# in strict.pm

    my %bitmask = (
+   stringify => 0x00000004,
    refs => 0x00000002,
    subs => 0x00000200,
    vars => 0x00000400
    );
    
    sub bits {
        my $bits = 0;
        foreach my $s (@_){ $bits |= $bitmask{$s} || 0; };
        $bits;
    }
    
    sub import {
        shift;
-       $^H |= bits(@_ ? @_ : qw(refs subs vars));
+       $^H |= bits(@_ ? @_ : qw(refs subs vars stringify));
    }
    
    sub unimport {
        shift;
-       $^H &= ~ bits(@_ ? @_ : qw(refs subs vars));
+       $^H &= ~ bits(@_ ? @_ : qw(refs subs vars stringify));
    }
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As you can see you could leave strict alone and just doe $^H |= 0x00000004 to set it.

Actually, PL_hints is just used at compile-time, not at runtime. But using (PL_curcop->op_private & HINT_STRICT_STRINGIFY) instead should work.

UPDATE: Oh, and a minor note: Perl_warner needs an additional argument that indicates the warning category, like:

if ((PL_curcop->op_private & HINT_STRICT_STRINGIFY)
                && ckWARN(WARN_MISC))
    Perl_warner(aTHX_ packWARN(WARN_MISC),
        "Stringification of reference disallowed");
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or alternatively you could omit the check and use Perl_warn which takes no such argument.

I did say it was untested :-) I only do enough internals to get my XS to run and admit to a rather cursory examination of the source. I do think the warner syntax is valid though (at least on 5.6.2)

$ grep Perl_warner op.c

./op.c: Perl_warner(aTHX_ WARN_SYNTAX, "Found = in conditional, should
+ be ==");
./op.c: Perl_warner(aTHX_ WARN_VOID, "Useless use of %s in void contex
+t", useless);
./op.c: Perl_warner(aTHX_ WARN_BAREWORD, "Bareword found in conditiona
+l");
./op.c: Perl_warner(aTHX_ WARN_VOID, "Too late to run CHECK block");
./op.c: Perl_warner(aTHX_ WARN_VOID, "Too late to run INIT block");
./op.c: Perl_warner(aTHX_ WARN_REDEFINE, "Subroutine %s redefined",nam
+e);
./op.c: Perl_warner(aTHX_ WARN_VOID, "Too late to run CHECK block");
./op.c: Perl_warner(aTHX_ WARN_VOID, "Too late to run INIT block");
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