That is totally possible with the use of tags. There is a post here by @madstacks that posed the idea of using specific tags to start splitting POB topics into their own little niches.
For instance, if you wanted to write a post about spirituality, you can drop in the tag "pob-spirituality" and it'll appear there alongside any other posts with a similar tag. This would also work for "pob-mindfulness"
The community is still small but once people start adopting the tagging process we'll see categories and sub-categories appearing and possibly moderators/spokespeople for these smaller communities will arrive as an addition to the front-end in the future.