One of the key features that Android 10 has is the delivery of critical system upgrades and security patches via the Play Store. It is called Project Mainline and allows OEMs to push system-level modifications to user devices via the Play Store. This method is a part of Google's Project Mainline and is a lot less disruptive as it doesn't force users to restart their phone every time an update is installed.
Project Mainline also opens up the possibility for another exciting feature; the ability for users to 'test' system updates before committing to them. It'll be particularly useful in enterprise environments as it allows administrators to monitor better how apps will behave after a certain update is installed. It'll also be useful for OEMs as it'll allow them to pull buggy updates a lot faster.
How does it work?
The concept is based on Project Treble's A/B partition concept, and it works by creating a temporary system partition which lets you run a build without installing it. This feature works in conjunction with Generic System Images (GSIs) which are stripped Android releases that run on all Treble-ready phones. GSI's work on a similar principle and are effectively wiped from the device upon reboot, restoring the phone to its original build.
XDA Developers spotted an AOSP commit titled "Mount multiple DSU partitions when present." which details how DSU (Dynamic System Updates) partitions can include product and OEM-specific information in the future. For example, the 'test' build could have all the Android 10 essentials coupled with OEM-specific customizations such as OneUI. It can even be extended to major Android releases, according to a Google engineer.
The project is still in very early stages of development, and It'll easily be several more months before we hear anything about this. A lot of changes need to be made before it is feasible, and even after that, it boils down to OEMs' willingness to participate in the program. Ideally, we should hear more about this alongside Android 11, when it is released next year.