This could make Power Automate truly useful for lots of scenarios involving OneNote and beyond!
There's definitely a need to for triggers on update, and more granular trigger/action outputs than just at the page/document level. It must be at the level of actual content like with the Fluid framework (MS already work on making Fluid work in OneNote).
Just one example: when maintaining and collaborating on the team knowledge in OneNote, when a specific page is updated (e.g. adding a new reusable link with a note, i.e. paragraph with a certain tag), automatically post a bot notification to the related Teams channel.
Then we could use Power Automate to create selective rule-based sync of actual shared content across multiple notebooks/sections (that for various reasons need to keep existing separately).