It's not too much of a stretch to say that the HTC influence on the Google Pixel and Pixel XL is obvious. They take a number of external design cues from the HTC 10, to the point of looking fairly similar. As luck would have it, they seem to take at least one internal design cue from the HTC 10, as well; HTC's fondness for dot view and flip cases has made its way here, in the form of magnetic screen reactivity. The screen on both devices will shut off when a weak magnet is placed on it, and turn on when the magnet is removed. While the feature may be included as a "just in case", flip case makers can certainly take advantage of it.
HTC's devices are often compatible with both traditional flip cases, and dot view cases. The latter involves a special function that detects a specific type of case, being a dot view case, and displays a few bits of critical information like the time and temperature on the screen in such a way that it shows through the dots in the case. This allows users to glean valuable information from their phone without having to actually access it, while also having all of the benefits of a regular flip cover at their disposal. This type of case could definitely come to the Pixel lineup in the future, if the software for it is on board. Regular flip cases that shut off a device's screen when closed are, obviously, already fair game.
Google did not officially announce the presence of magnet reactivity in the screens of the Pixel and Pixel XL upon launch, which makes this feature that much more of an exciting find; it may go far beyond something as simple as a flip case or a dot view case. Google may be hiding more features under there, features that could enable a wider range of accessories that incorporate rich interactivity in unique ways using magnets. On the other hand, the feature could have simply been put in "just because" or "just in case" and not actually used in any official capacity. In any case, smart flip cases for the Pixel phones are certainly a go, and consumers will likely start seeing them fairly soon.