Some Chrome OS devices might get face detection features via a future update if a recent code commit to the Chromium Gerrit is any indication. The commit points to a test for code that will look for and detect faces via a Chromebook's built-in webcam and could only be intended for select hardware, explicitly making reference to the chipmaker's "Intel Face Engine." It's also very obviously still in its early stages since the current test primarily centers around whether or not the camera can detect faces and return a response via a "getResult()" method. In effect, it's currently being tested at the hardware abstraction layer. What's more, the commit's title reads "intel: ipu3: Add face detection" rather than pointing to any exact Chromebook boards or devices. However, if and when the feature does get implemented, it appears as though that will happen alongside the Android Camera application as well. So it may not be limited to Chrome OS hardware with Intel components at all.
In any case, the addition of face detection features wouldn't automatically point to any single software feature. For starters, if it's to be included along with a more robust camera app, it may simply be required in order for AR stickers, beautification, or other similar camera features to work properly. There are are also dozens of ways to use face detection and necessarily more likely than others. For example, it could also see implementation as a way to keep a Chromebook's lit and active as long as there is a face within the frame. Tying into that, software along those lines could go further to include facial recognition that would only allow that to work if a familiar face remains in frame. Beyond even that, the system could be used alongside A.I. for a more fully fleshed-out security feature based on recognition in order to make logging in more convenient.
Any of those could be used in conjunction with the others as well and there are plenty of other circumstances where detecting a face would be useful for developers on the platform. That's especially true with support for Android apps in Chrome OS now relatively common and Linux apps coming via a more widespread rollout within the next several months. With that said, there's no guarantee the code will ever be a full feature or make its way to any given Chromebook model.