New API functions are fine as long as they are available everywhere, but deployment does not happen quickly. The interfaces described as non-standard are just that, and are unlikely to be present anywhere but systems with the NRL IPv6 code or with the (NRL-derived) Linux inet6-apps kit. The standard new interfaces are supposed to be present now in AIX, BSD/OS, FreeBSD, Linux (with GNU libc 2.1), OpenBSD, NetBSD, Solaris, and Tru64 UNIX. In addition, IRIX and HP-UX will probably adopt these functions very quickly (if they haven't already). In summary, all modern UNIX systems are expected to support the standardized interfaces now or very soon.
But what about legacy systems? The good news is that there are fairly portable implementations of these functions that run on legacy systems and can be included with programs. Several free implementations of the new interfaces exist, and are reasonably portable. There are already some free software packages, such as Zmailer, that have used this approach.