My suggestion is: the Notification option "Only show selected feed", can be changed in "Don't show the selected feed"?
The above notification setting is in: Tools > Settings > Notifications
This is my idea:
1) select which feeds I don't want to be notified
2) create a filter for the same feeds and set to be notified if some condition match.
Yes, I know, I can do it also now... selection "Only show selected feed" and create the filter... quite similar, but...
in this case, everytime I add a new feed, I need also to remember to update the "Only show selected feed" optinon to include the new feed.
Instead, if the option is "Don't show the selected feed", the option need to be update only if I want to exclude it from notification.
It make sense to you?