Fir of all sorry for my bad English, I hope you will be able to understand me. The 2-level category limitation seems to prevent from building of comprehensive community category hierarchy. Does anybody here have experience with such communities that need more than 2-level of categories?
You can use the tagging plugin (integrated by default), users can watch, track or even mute some tags, they’re easy to use. They can be a good addition to the 2-lvl categories
Using too much sub-categories wouldn’t help the user experience IMO. The category breadcrumb (the all categories on latest) and the hamburger menu would be overloaded