Metaballs are way too expensive.
> SPH ... with 500 000 particles ... about 2.5 fps on my GTX 1070
Still slower than what CNCD & Fairlight demonstrated in 2011 with "Numb Res", at 120fps (stereo 3D) on a geforce 280:
> The demo features up to 500,000 particles running under 3D SPH in realtime on the GPU, with surface tension and viscosity terms; this is in combination with collisions, meshing, high end effects like MLAA and depth of field, and plenty of lighting effects
On a related note, one of the annoying things about metaballs for fluid surfacing is that there's some spooky action at a distance. Two drops of water will reach out towards each other as they come closer together, which makes no physical sense at all.