Thank you for answering my post and for your input! I do understand your issues with AI being overhyped and a buzzword.
My intention in implementing AI features is not to follow the trend but to increase productivity and decrease users' mental effort. For example, in some posts here in the community, a user said that he has ADHD and that summarizing and tagging notes may help him with organizing notes.
You could use graph-based algorithms to create an extractive summary. However, I am trying to create an abstract summary in my proposal, so I need to use ML for that. As I am thinking right now, I might also give users an option to create extractive summaries. Also, you don't have to worry about privacy at all. It's all happening on the client side.
I am currently proposing to integrate it with the core application. Still, it might also be a good idea to propose it as a plugin and then decide with the Joplin team which is the best option (taking into account the community's opinions and perspectives 
).