There are reports that OK Google is going to be removed from the Chromebooks in order to make way for Google Assistant. This was discovered by ChromeUnboxed that Google is working on getting the new and upgraded assistant to the devices. Although this feature is rarely used in the devices, it can still be found in the settings section.
There might not be many people that use voice assistance, but it a feature that is slowing warming up to consumers and would be a waste for Google to remove it completely. This is another sign why Google Assistant will be seen on the devices as there is also a shortcut key (Search+A) to call up the feature, which they are working on and bring it to all Chromebook devices, the usual keyword is still available but it might activate all Google devices that you have in the house or around you.