It's 2020 - Oracle Adds Meson Build System To Solaris
As usual for Solaris 11.4 SRUs, it's mostly stable version updates for included packages and other package updates stemming from security issues. With Solaris 11.4 SRU19 this means Cython 0.29.14, MySQLClient 1.4.5, Git 2.19.3, Python 3.7.5, PHP 7.3.14, Firefox 68.5 ESR, and other mostly mundane updates.
There are a few new Python packages added to the OS with SRU19, but nothing overly exciting. The main addition for SRU19 is arguably the introduction of a Meson package.
The Meson build system has been around for more than a half-decade and in recent years has seen widespread GNOME adoption, important FreeDesktop.org components like X.Org and Mesa have also begun relying on Meson, and countless other open-source projects moving to it as well. So now finally in 2020, Meson is officially offered by Oracle Solaris 11.4 SRU19.
Then again, most corporate users of Solaris aren't using it for bleeding edge software but rather legacy stable software deployments, so the big delay isn't too surprising. With so many upstream projects moving to Meson as their preferred build system, it was inevitable that eventually it would need to be embraced by Solaris. Upstream Meson has supported Solaris/Illumos along side its support for Linux and other Unix-like platforms, Apple macOS, and Windows. The great cross-platform support is one of many selling points for Meson.
More details on Oracle Solaris 11.4 SRU19 via the Oracle Solaris blog.