It’s easy but a bit data intensive. Take two 3D splat images at different times, optimize them, then interpolate from the first to the second. Repeat at intervals. Now you have a video. A full moving subject is about 500Mbps, although it depends a lot on the quality of the source images that you make the 3D splats from and how detailed the output image is. Search for “4D gaussian splats” to find references.

That's just animation like an animated GIF: a series of static frames. What's more interesting is animation in the sense of deformation, as in skeletal/skinned meshes. These deformations require minimal data and can be generated dynamically.