I have been wondering about liquid cooling since noticing mention of it on the forum a short while ago.
I think we have a problem in that any such solution would be inefficient. Too much energy is going into warming the water - so to speak. This also applies to heat sinks to a lesser degree. Both solutions add to the nozzle size.
Perhaps the crux is a suitable thermal break. We need to concentrate the heat in the melt zone/nozzle.
probably mentioning the obvious.
I am afraid I have no solution or 'currently' the means to explore. Still need workspace.