I don't think there at least should be a separate forum, per se. Livewire already stated a page back that D&D currently is already a makeshift T-Dome. So as a result, this idea could be approached one of two ways:
Make a forum specifically for sex/nudity/other topics, as Antemortem already stated. That, or if you don't see a need for a separate forum, then lift the censors off D&D so those kind of discussions would take place there. I do hope that people here are level-headed enough to discuss sex without an issue, so maybe this could be a possibility?