My understanding is that as the Train Operating Companies' contracts come to an end different parts of the railway will be brought back into public ownership. This will take about four years.
What will be interesting to see is whether any compensation will be paid out. If so, this has the potential to slow down or even prevent other public utilities being brought back into public ownership.
However it's done it's likely that the same people will be running the same locos and rolling stock for e.g., but will be directly accountable to the government rather that some shadowy shareholders who are quick to take the dividends but slow to invest.