Of course it will be a decade before everyone updates to a version that supports this option and allows the user to enable it. In the meantime we'll have our time and attention wasted for years (T_T)
There's another, automatically getting spammed with emails and then having to manually opt-out. I get you want it to be frictionless but when signing up a opt-in checkbox for email would respect my time and scarce attention than opting me into daily emails and forced me to later opt-out.
And sorry to pick on Discourse. There's tons of other offenders but Discourse is one most people on HN have experience with. Steam/Xbox/Playstation all have the same issue. Wasted time and attention required for things I don't care about. The worst is the OS popping up achievement notifications right over the climax of some scene. That others care is fine. Just let me turn them off because "Attention is your scarcest resource".
As a user, I don't want to be bombarded with distracting emails and notifications every time I join a new board.