Cum fluid physics
A lot of companies are experimenting with realtime volumetric fluid simulation for creative software, but as I understand it, a simplified version might be possible in a game as well. I think it would make for an amazing selling point, as I don't think any other NSFW games currently have full-blown fluid simulation. Ideally it would have customization for things like stickiness, stream thickness, velocity and flow, viscosity, surface tension, etc.
It's probably a pipe dream though, as the amount of work required to fully implement something so advanced would probably take years.
I honestly reckon we'll get around to it eventually, granted that this project survives long enough. It won't happen for the foreseeable future though, as we have a lot of other features planned. But fluid dynamics against both environment and characters is becoming more and more feasible each passing year as hardware and software develops. I'd argue the biggest challenge with fluid dynamics in our context would be collision against animated characters, but that challenge is more or less already solved thanks to SDF baking, which can be done very quickly (all things considered). The biggest problem with SDF baking is the communication between GPU and CPU, but for a fluid simulation running on the GPU, that communication would not be necessary.