Right now custom filters are disappearing after reloading the SN web-app. I suggest to add a way to ‘pin’ filter to make it persistent. This is especially important if saved search request will be implemented.
Persistent filters is an interesting idea. We are thinking of saving your preferences for filtering depending on your the current target (A Parent Card or Home etc.) of the Noteboard? Would that suit your use-case?
Of course, this is even better: to have specific filtering based on card context.
Filters are now persistent with the introduction of Offline mode in Supernotes 3.0.0.