A recent change to the Chrome OS code repository indicates that Google is working on giving users the ability to take notes from the lock screens of their Chromebooks. The code repository mentions that some of the changes made were actually fixes for some earlier broken code regarding how stylus input on the lock screen is handled, which means that this feature has likely been in development for a little while. The code entry calls for retiring a previous version of the stylus on lockscreen system call, and replacing it with a new, more universally app-friendly version. Rather than checking only for stylus removal, it will now check for any pre-specified activity, and launch an app of choice when it's detected.
The newest version of the code handles stylus input a bit better, and even includes a bit that could allow lockscreen note taking on non-stylus Chromebooks, as well as opening up a given app on the lockscreen when a stylus is pulled out. Essentially, it's a custom action button that can be triggered in a number of ways, and allows the launching of almost any activity on the lock screen. On top of no longer limiting the preferred triggering action to a stylus removal, it adds in some code that allows either the trigger action or a stylus removal to trigger something. This means that in the near future, Chromebooks with styluses included, such as the Samsung Chromebook Plus, could launch one app when removing the stylus on the lockscreen, and another when performing a given trigger action.
This new function in Chrome OS fits nicely with the beginning of what could be a wave of stylus-equipped Chromebooks, but also serves to spice up the lockscreen a bit and give users a more convenient overall experience whether their Chromebook of choice is equipped with a stylus or not. In any case, the code is still not active yet, and there seem to be no explicit calls to the new code aside from the old code, and the notation that the new code is being implemented. This, of course, means that even in the absolute latest build of Chromium OS, the functionality is not included just yet. There is no timeline for when it may come, either.