I do understand the reasoning that page models are not loaded in the panel (and thus in hooks). The kirby()->models() does not work for me either unfortunately. Any other ideas on how to get the page as instance of the correct page model inside a hook?
As a sidenote: It might also be worth changing the docs for page models, where it currently says
This page model will be loaded every time Kirby encounters a page of the given type (so project in this example), whether it is in a template, a snippet or anywhere else.