tye was quick to point out an easy solution for the problem was to use a parallel hash as a lookup table. I admitted it was a good straight forward answer but defeated my purpose. On the other hand if an anonymous sub can be made to take up less space than the anonymous array:

sub compact {
    my $ref = shift;
    my $pck;  # Packed information except reference

    # purposefully avoiding dispatch table
    # This keeps us at HoC
    return sub {
        if    ( $_[0] eq 'data' ) { return $ref };
        elsif ( $_[0] eq 'blah' ) { return unpack('A1', $pck) }
        # where each unpack format gets desired data
    };
}

$hash{foo} = compact( [1..10] );
$hash{foo}->( 'data' )[3] = 42;
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The interface could use work and it doesn't really explore any uncharted territory for me. It also is still not a single hash. We are just trading anonymous subs for anonymous arrays.