Here is a patch (applies to 5.3.1 ext/standard/dns.c) 

If ipv6 is enabled, it will try first and fallback to ipv4 resolution if no record is found.

--- dns.c.orig  2009-12-23 05:13:19.000000000 +0100
+++ dns.c       2009-12-23 05:17:14.000000000 +0100
@@ -251,16 +251,27 @@
 {
        struct hostent *hp;
        struct in_addr in;
+       char* txt_addr;
+#if HAVE_IPV6
+       char txt_addr6[128];

-       hp = gethostbyname(name);
+       hp = gethostbyname2(name, AF_INET6);

        if (!hp || !*(hp->h_addr_list)) {
-               return estrdup(name);
+#endif
+               hp = gethostbyname(name);
+               if (!hp || !*(hp->h_addr_list)) {
+                       return estrdup(name);
+               }
+               memcpy(&in.s_addr, *(hp->h_addr_list), sizeof(in.s_addr));
+               txt_addr = inet_ntoa(in);
+#if HAVE_IPV6
+       } else {
+               inet_ntop(AF_INET6, *(hp->h_addr_list), txt_addr6, sizeof(txt_addr6));
+               txt_addr = txt_addr6;
        }
-
-       memcpy(&in.s_addr, *(hp->h_addr_list), sizeof(in.s_addr));
-
-       return estrdup(inet_ntoa(in));
+#endif
+       return estrdup(txt_addr);
 }
 /* }}} */

any progress on this?

Please, Add IPv6 support in gethostbyname

Probably gethostbynamel() which already returns a list? Or gethostbyname2() to mimic what the underlying system uses?

But still not having IPv6-support in 2020 sounds wrong.