I don't want to rush it or create additional pressure for you guys, but just came here to agree that this is maybe the most important feature that other forums have, but wpForo doesn't have.
In an era of Game of Thrones final season, spoiler tag in posts is must have. I've seen so many wpForo forums that struggle without it, including mine with few hundreds active users per day.
We need just simple spoiler tag wich would hide text, just like in wpDiscuz. And I think that it would be appropriate even as paid addon.
How to hide a spoiler text to guest users