I'm personally not against such a feature, but... To have posts automatically scanned, you need to choose a service that will do this. Today, almost all services for detecting content written by AI are far from perfect. Which one should you choose if all of them can produce erroneous detection? There will be a large number of threads on Meta with outrage from users who disagree with their posts being labeled as AI-written. At one time, by the way, I gave examples of AI text detection services mistakenly recognizing innocuous text as AI text.
Is there a superior one? What you could have is it just alerting the user that their post had been detected at whatever percentage and to urge caution before posting or only consider posting if they haven't used an AI tool.