what you're a describing is a half-assed feature usable only for your "scenerio" which everyone else can just turn off.
to make this truly useful for the rest of the ~10k people using tt-rss.apk right now it'll have to be a lot more flexible than that, for example configurable on a per-category or a per-feed level, etc etc. and this is just not something that i'm interested in implementing at this point. in my opinion it's better to not have a feature at all rather than have a half-assed one.
however, nobody is stopping you from making a "tt-rss notifications.apk" and publishing it on play store, i can suggest you do that instead. additionally you'll learn what a wonderful platform android is for a developer.
e: your actual problem of being notified for stuff you might consider interesting off low-traffic feeds can be solved using a widget showing fresh articles and filters, so far i'm not convinced why a catchall duplicate method to do the exact same thing is needed. "other apps do it" is not a valid justification.