The latter to in part support the former.
The benefits to developing standard and optional subcommands separately from the core include:
- Improves its quality and the developer experience.
- Having the possibility of offering both a native (
sync) and compatibility (rsync) subcommand is good. Moreover, there are several ‘eras’[0] of rsync in wide distribution, due to issues such as licensing, and supporting externally developed and maintained subcommands for interface variants would be trivial. (rsync26) - I can envision CLI subcommands as a useful extension point for those developing for SAFE.
[0] “rsync version 2.6.9 protocol version 29; Copyright (C) 1996-2006” is what’s included with macOS Mojave.