One of two conditions must be satisfied in order to create a board:
1- there have to be sufficient number of threads about this topic in other boards to the point where that board is full of those kind of threads,
2- (for local boards) there is a large megathread.
These are from my own observation and are not in any rules or moderator posts or anything like that.
I know that these are the (unwritten?) rules for new subforums, but I don't completely agree with them.
When you 'are your own bank', especially for newcomers into the whole field, having a place to find educational materials about basic cybersecurity practices (topics such as: how to secure your machine, proper backup practices, encryption guides, signature guides, pgp guides, ...), while also being a place for asking questions.
You and I wouldn't believe at what kind of basic level most people struggle with even using computers. Meanwhile we encourage them to be their own bank, without even having a central place that teaches them security concepts and decreases the likeliness of them losing it all.
To get back to my view on
rules for new subforums: I do think that in some cases, people don't even bother creating threads about some topics, if they know they belong and will be buried immediately in off-topic, altcoin discussion, or something like that, where they won't get useful interaction and opinions. They will just go somewhere else. As a matter of fact, I sometimes just choose to talk to people in private about Lightning related stuff, since we don't have a Lightning board.
Therefore, it
could (this is a hypothesis) be the other way round: creating a subforum, even without existing megathreads, may encourage and attract discussion about that topic. I personally believe that Lightning and Cybersecurity would be two boards where this could take place.