I wonder if each variables with ext magic has its own virtual table pointer.

It does! That means that having only one extension type is not as limiting as it seems!

use strict;
use warnings;

use Inline C => <<'__EOI__';


static const char* test1_str = "Hello, ";

static int test1_mg_get(pTHX_ SV *sv, MAGIC *mg) {
    sv_setpvn(sv, test1_str, (STRLEN)strlen(test1_str));
    return 0;
}

static const MGVTBL vtbl_test1 = {
    test1_mg_get,
    NULL,
    NULL,
    NULL,
    NULL
};

SV* get_test1_var() {
    SV* sv = newSV_type(SVt_PVLV);
    sv_magicext(sv, NULL, PERL_MAGIC_ext, &vtbl_test1, NULL, 0);
    return sv;
}



static const char* test2_str = "World!";

static int test2_mg_get(pTHX_ SV *sv, MAGIC *mg) {
    sv_setpvn(sv, test2_str, (STRLEN)strlen(test2_str));
    return 0;
}

static const MGVTBL vtbl_test2 = {
    test2_mg_get,
    NULL,
    NULL,
    NULL,
    NULL
};


SV* get_test2_var() {
    SV* sv = newSV_type(SVt_PVLV);
    sv_magicext(sv, NULL, PERL_MAGIC_ext, &vtbl_test2, NULL, 0);
    return sv;
}

__EOI__

use Devel::Peek qw( Dump );

my $test1 = get_test1_var();
my $test2 = get_test2_var();
print("$test1$test2\n");
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