Wikipedia has a surprising amount of info on the solar system's icy worlds. I think it helps to look at all of them in evaluating Ceres's chances. I only became aware of the potential for an ocean on Ceres a few weeks ago when looking up some data on it and saw that in the wikipedia entry. I didn't even include it on a list posted a few weeks earlier on places where we might find life. Turns out Ceres is pretty unique in the asteroid belt do to it's low density. It's actully pretty similar to Ganymede, Callisto, Triton, Titan and Pluto in composition. We now strongly suspect 3 of those have a liquid layer plus the potential for a subsurface pool of liquid on even smaller Enceladus so I think it's a real possibility although there are a lot of factors involved in those other worlds having oceans. Composition may be a big factor for Titan (along with size) and Enceladus, gravity for Europa, and size for Ganymede and Callisto.

Ceres
Enceladus
Europa
Ganymede
Callisto
Titan

I posted pictures of the structures roughly to scale here Surprisingly it looks like Europa has a rocky core about the same size as Ganymede's and Io would have been by far the biggest if it had retained as much water as Callisto or Ganymede. They don't show an iron core for Titan, and I don't know if it's intermediate between Callisto and Ganymede in differentiation or they just don't know. They show a thinner mantle so that might mean the core is less dense to give a similar density.

Regards,
Mark