Android O will allow users to pause a system update and return to it later
As it turns out, the latest developer preview of Android O (which is the second such preview) has a useful feature that will allow you to pause a system update in its tracks, and continue it later from where you left off. This can be used in case your battery is running down, or you've lost connectivity and you need to find a new Wi-Fi or carrier signal. The feature is available regardless if the update is a large or small one.
According to Google engineer Elliott Hughes, the "pause update" feature is part of a Play Services update. A similar feature has already been a part of Chrome's built-in downloader ever since Chrome 50.