I think you're off to a great start with the MetaBalls, granted there are issues/limitiations to deal with.

MetaForm was a great plugin back in it's day, certainly was great for animated fluid/smoke/flame effects. I keep thinking it used a basic directional particle(sphere) emitter prop or emitted from the surface of a figure, with particle lifetimes, direction/spray radius controls, plus collision witn non particles etc.

Looking forward to seeing what you manage to come up with.  I'm not expecting another MetaForm, I think the scripts you've already created are awesome contributions, still amazed these are free.

Would be cool if some of the other gurus joined you and pooled resources(I see you caught BB's eye there), wonder if PhilC or face_off could offer any input.

So, whats next after MetaBalls?!  Perhaps a fracture system for dynamicly destructable objects/scenes.. Hah.