@evan I'm unsure if a manual filter option would solve the intial confusion, seeing as at least in your PR the filter is not enabled by default and people tend to not change away from it.
Also it seems that this filter is for all notifications, not only for boosts. Not noticing a bot (or people abusing the tag) replying with some weird stuff to your posts would be a major issue. In my eyes this needs a more fine-granular setting
(Or as I suggested: Not send notifications to the user at all when "boosting" in an automatic way. I personally do not see the value of what is basically providing the same functionality as hashtag following sending notifications when hashtag following itself doesn't.)