You could launch it today if you felt like it, but only if you charged money for it and paid moderators to enforce an AUP.
It's trivial to write such a thing, but someone has to host the content at an https:// endpoint for browsers to access it, and so someone has to pay money for hosting, and someone has to charge users for it, which means enforcing an acceptable use policy, which requires staffing abuse reporting and moderation to keep up with usage, which requires charging users for that, too. Anyone who tries to skip any of those steps ends up going broke and shutting down or losing payment and hosting providers. And you might still find that the target market for this is very small (thousands of users worldwide), or that the target market is largely unwilling to tolerate enforcing a code of conduct. And don't forget the guaranteed lawsuits from companies who think they have a right to disallow you from recording comments about their site! Oh, and spammers and abusers, you'll have to have a plan for dealing with those, except that your target market may be largely unwilling to tolerate identity verification checks (simply charging money isn't enough).
None of this is an obstacle to launching a site that charges users from day one to participate, as long as you build it lean, with a cost model that effectively scales as users participate, and with a working anti-spam/abuse model. It's just that most modern startups want to launch with a 'free' tier, and that's simply not compatible with this idea on the modern anonymous internet.