It is rather more rocky than that. (pkgng arrived in FreeBSD 9.1, by the way. Not 10.)
* pkgng has some stark differences to OpenBSD pkg, most notably the notion of Debian-like "post-install", "pre-remove", et al. scripts.
* The systems compress packages with different tools. OpenBSD pkg uses gzip. FreeBSD pkg uses xz.
* OpenBSD has a notion of "package flavours" that does not really have an analogue in pkgng.
* The introduction of pkgng was distinctly problematic. A lot radically changed in early versions, most critically the configuration file format. It used to be YAML. It's now UCL.
* The documentation is misleading to the point of being downright wrong. The FreeBSD wiki still insists (https://wiki.freebsd.org/pkgng#Metadata) that the configuraton file is YAML. The manual page for pkg-create gives examples such as "name pkg-name" and "file sha256-hashpath", which is syntactically incorrect for either language and the wrong keyword to boot. Following the manual does not produce a working configuration file. Ironically, the wiki provides better information on this, even though it provides that information in the wrong configuration language.
* The documentation is misleading to the point of being downright wrong. The FreeBSD manual page for pkg-repository claims that repositories contain files named packagesite.txz, repo.txz, and filesite.txz. In fact, the pkg repo tool generates files named packagesite.txz, meta.txz, and digests.txz .
* OpenBSD pkg and FreeBSD pkg don't really have a common notion of "package repositories". The ways to organize pulling packages from remote storage locations are quite different, even down to the fundamental file fetching tools. FreeBSD has fetch. OpenBSD has ftp.
All that having been said: the idea that a unified packaging system necessitates a unified codebase is disproven by Ubuntu and Debian. (An example is OpenRC: present on Debian 8 at https://packages.debian.org/source/jessie/openrc, up to version 0.21 in what is to be Debian 9, and gone from Ubuntu 16 at http://packages.ubuntu.com/xenial/openrc) Conversely, one can have a unified codebase even with multiple packaging systems.
This is all true, but I was mostly comparing the pkg_* tools (pkg_add, pkg_info, etc.) that were used before the arrival of (NetBSD's) pkgin or (FreeBSD's) pkgng (does OpenBSD have something similar? If so, I haven't used it at this point).
* pkgng has some stark differences to OpenBSD pkg, most notably the notion of Debian-like "post-install", "pre-remove", et al. scripts.
* The systems compress packages with different tools. OpenBSD pkg uses gzip. FreeBSD pkg uses xz.
* OpenBSD has a notion of "package flavours" that does not really have an analogue in pkgng.
* The introduction of pkgng was distinctly problematic. A lot radically changed in early versions, most critically the configuration file format. It used to be YAML. It's now UCL.
* The documentation is misleading to the point of being downright wrong. The FreeBSD wiki still insists (https://wiki.freebsd.org/pkgng#Metadata) that the configuraton file is YAML. The manual page for pkg-create gives examples such as "name pkg-name" and "file sha256-hash path", which is syntactically incorrect for either language and the wrong keyword to boot. Following the manual does not produce a working configuration file. Ironically, the wiki provides better information on this, even though it provides that information in the wrong configuration language.
* The documentation is misleading to the point of being downright wrong. The FreeBSD manual page for pkg-repository claims that repositories contain files named packagesite.txz, repo.txz, and filesite.txz. In fact, the pkg repo tool generates files named packagesite.txz, meta.txz, and digests.txz .
* OpenBSD pkg and FreeBSD pkg don't really have a common notion of "package repositories". The ways to organize pulling packages from remote storage locations are quite different, even down to the fundamental file fetching tools. FreeBSD has fetch. OpenBSD has ftp.
All that having been said: the idea that a unified packaging system necessitates a unified codebase is disproven by Ubuntu and Debian. (An example is OpenRC: present on Debian 8 at https://packages.debian.org/source/jessie/openrc, up to version 0.21 in what is to be Debian 9, and gone from Ubuntu 16 at http://packages.ubuntu.com/xenial/openrc) Conversely, one can have a unified codebase even with multiple packaging systems.