Interesting...
Hi LJK
Andrew Prentice's Modern Laplacian Theory predicted most of that a few years ago in the wake of Galileo, though he wasn't so keen on there being subsurface oceans because the thermal gradient needed meant there would be solid-state convection long before the ice melted. He proposed remnant magnetism in Ganymede's core instead and salty ammonia/water fliud in Callisto.
Adam