I've been working on a solution to this:
It's probably our biggest user complaint right now. We've been bikeshedding back home, and I think it's ready to run it by the larger NodeBB community for some feedback.
It changes the current design of two states to three, adding a new state called "Ignoring." And so, instead of toggling with buttons, I've turned it into a dropdown, which has the added benefit of displaying the current state, not the opposite state of the thread:
In addition to not showing up in the unread feed, ignoring a thread keeps the unread styling from applying to the thread in other lists (e.g., recent, categories).