You say that China forbid mining; I say, why not going one step further and forbid its use too? Maybe even take the heads of the disobedient? That should definitely discourage the rest do so. Why should the people use a currency that decentralizes the economy when their political regime requires the exact opposite? Trust to the pigs.
So, here's my counterexample to your assertion: What if China decides to ban every cryptocurrency, including the PoS ones, as a cause that it's a threat to (their) people?
I anticipate there will never be more than 100K nodes, probably less. It will reach an equilibrium where it's not worth it for more nodes to join in. The rest will be lightweight clients, which could be millions.
At equilibrium size, many nodes will be server farms with one or two network nodes that feed the rest of the farm over a LAN.