It’s a matter of having enough posts and comments to have additional subs or communities.
The mod of this one @ValueSubtracted has replied to other similar questions that, as there is volume and interest, other communities (subs) can be added here.
(I previously posed the same question about establishing a Treklit or trekbooks one.)
There’s definitely and interest and an open invitation to mods of other Trek-related subreddits, to set up and find a home here.
For now, the three communities that exist cover the waterfront from more serious to humorous, with the general StarTrek one also being the meta discussion for the community.