We do have off topic board and I'm pretty sure you are aware of it but we allow vanilla subject. Shouldn't you elaborate about your kind of "off topic"?
Regardless of what topic it is, there can always be a chance for someone to post a something that could derail the topic, and therefore it could encourage escalation. The moderation has gotten better on handling toxicity, and because of this perhaps an off topic section isn't a big deal. You have explicitly mentioned you do not allow for ''racist'' discussion which in return could be interpreted as political correct. Which i have personally adhered to and respected here on TUS. But again there could be a topic about a world event or whatever else controversial that could surface for discussion which also could cause heat between people.
Example of this is of the recent topic that got deleted because it lacked civility. Is Trump considered a racist topic? I am certain there could similar Instances in the future, especially if maps of such content could spawn. That's why I made this topic. To get a clear picture on the matter.