Hi Guillaume @Dagens, you can implement 3D Metaballs using Signed Distance Fields.
However, the approach will require volume raymarching, which won't run smoothly on 2024 Spectacles hardware. I've tried many optimizations tricks and one that worked decently was view-dependent 2D metaballs. I've also been thinking on some particle-based approaches which, if cleverly done, could produce quite convincing 3D metaball results. Let me know if you need some additional info on implementation specifics.