Last year, I wrote a blog about AnyNet support (actually, the lack of it) in the 7.1 release. If you carefully read the IBM planning statements, you will also find planning statements regarding SNA in general; way back in 2008, IBM published a planning statement on future SNA support. You can find it at the very end of the Future Software Planning statements. Even though these planning statements have been published, from time to time I still get questions about SNA support on i or hear rumors that SNA applications won't work at some point.
SNA (Systems Network Architecture) has been a part of the operating system since the S/38 days and continues to be there, although over time certain features and functions have gone away. In general, when you see functions that no longer work, it's due to external hardware dependencies that don't have replacements from IBM.
For “native” SNA support in OS/400, i5/OS and IBM i, low-level support of the SNA architecture was part of the I/O Processors (IOPs) that were attached to the system. In particular, the “DLC” (Data Link Control) layer of the SNA protocol was implemented in the IOPs. With the more recent hardware, IBM has moved away from supporting IOPs and is just using I/O Adapters (IOAs). With this change, the DLC layer of software that SNA was dependent upon was no longer available. Rather than re-implement the DLC layer in the operating system, IBM chose to use other technologies to support the SNA applications – AnyNet and then Enterprise Extenders; these allowed applications based upon the SNA protocol stack to run over TCP/IP networks.
Also in the past, there were many different flavors of link-level protocols – Token Ring, Ethernet, ISDN, ATM, Frame Relay. X.25, etc. Most of those protocols have also disappeared over the years and today, Ethernet is primarily what everyone uses to connect their systems to their networks.
It's safe to say that in the future SNA-based applications will continue to be supported. SNA-based applications include things like SNADs, Display Station Passthrough, DDM, ICF applications, etc.
IBM i documentation on SNA is all still available. In the Information Center, you'll find it under Networking->Network Communications. The documentation that was never incorporated into the Information Center is also still available and references to it can be found in the “Related Information” section.