Also, we need to take in consideration that some themes are more popular in some languages and non-existent in others. Here is where I suspect tags can help alleviate the category-creation-need and opt for a more organic growth, where only when there is a significant volume of topics around the same theme that become distracting for other topics in the same category, we create a new subcategory for that.
How to make decisions about this? I guess we’ll have to rely on language-communities to self-organize and decide what’s most effective for them, rather than a global policy?