I'm confused why you would think so. Did you mix up your links? The paper you link to replaces the quick-and-dirty 3D-to-2D approximation used in Gaussian splatting with more physically accurate rendering using Monte Carlo path tracing. FreeTimeGS uses Gaussian splatting for 3D scenes with movement.

Both descend from (and cite) 3D Gaussian Splatting for Real-Time Radiance Field Rendering https://arxiv.org/abs/2308.04079 but take it into entirely different directions.

Now add VR into the mix...

People often say this about vr, but I think the truth is that consumers of adult videos are not motivated enough and the production costs outweigh the benefits. The demo scenes here were each captured on about 20 cameras, each carefully synchronized and rigged to be out of each other's lines of sight. Add the expertise and time to train the models (still more like pets than cattle) and we're getting into movie ticket territory and away from tube site