While I applaud any effort to increase discoverability on the site and I also understand the need to present the content more professionally and curated I do wonder. Any fixed system of categories will have gaps in them. The idea that a model can only belong to one category certainly has its merit. It does force you to focus on the one thing the model represents. But I'd argue that none of the models on Sketchfab, or any other 3D platform for that matter truly belong to one category unless that category is called "stuff" or "things".
Let's try this out: I have an anatomically correct model of Angela Merkel, rigged and normal mapped for a game. Should it go in "News & Politics", "Characters and creatures", "People" or "Science and technology"? How does picking one category make the model more discoverable?
Of course this is a rigged example, but try to find a model which isn't suitable for more than one category. The Hamburger example in this article for instance. It obviously is food. But the model is made for augmented reality (it says so in the title). That should justify a place in "Gaming". And you could also argue this type of food is US "Cultural heritage & History".
I'm not against categories at all. The new categories page is beautiful and very inviting to browse around. But I can't help feeling allowing only one category per model is more exclusive than inclusive. And also, some categories seem to be missing, such as the earlier mentioned weapons, or toys, sci-fi or educational models. And what about models where the focus is to evoke or depict an emotion and not a thing? Where's the category for love, anger or friendship?