Indeed, the whole point of this thread started from the question of what sort of temperatures and pressures would we be dealing with if a world had liquid methane oceans. In the viewpoint you describe, the actual material shouldn't be described at all aside from noting that it is not water as describing it as methane means that the behavior should fit within our experimental observation of methane and understanding of thermodynamic properties and implications for pressure and temperatures of the environment, which might run counter to some of the other randomly determined properties of the world.