Sounds like an overkill, since watched threads is enough for *most* cases
My impression is that when you have two functions that do almost the same, the user gets really confused and only the hardcore users know which is which and what the difference is. We already have watched threads for that ...
Looks like something for an addon instead
FWIW, I do watch every thread I reply, but after a while when people start talking unrelated things (which always happens) I stop following that thread.
My use of watched threads is use of the existing functionality for what it was meant to do, not an endorsement of this proposed filter which I see myself as feature creep, thought we can disagree on that