The Verge reports the update includes a "Boost Mode" on PlayStation 4 Pro systems, which allows them to run "at a higher GPU and CPU clock speed" to improve performance for games released before the Pro was, allowing for reduced load times and higher framerates on some titles. The mode could cause glitches or errors in some games, however, which is why the mode can be turned on or off in the system menu. Currently, games released before the Pro run about the same on the system unless they're updated by the developers, and in some cases run worse. Though Boost Mode wouldn't give older games HDR options or allow for higher texture density, it should be a nice quality-of-life improvement.
We will keep you informed once we know more about this update.