The privatisation of the train system hasn't worked I agree and companies have taken unwarranted profits as a result I agree but that is where the correlation ends.
We will not be able to nationalise the train franchises and then the removal of 'profiteering' suddenly fixes the system. The only benefit of nationalisation really is to make things more efficient through centralisation. There could be a more flexible workforce by working as one company for example although naturally the unions will be against anything that improves efficiency or flexibility.
You only have to look at the DfT last resort operator, it made £2.2bn last year however only achieved £20m profit across 4 operators, it's not exactly a lucrative business. The profits come from subsidies but DfT isn't going to subsidise itself so all it will do is save money and that is bound to be absorbed as savings for something elsewhere.
If we want a properly working system then we need to invest in it, that means putting in far more money than is extracted as profit and unfortunately I'm not sure where that's going to come from. The idea that we will just nationalise the franchises and then suddenly have a perfect system with cheaper ticket prices is just lunacy.
The reality is the TOCs will be wound up and we'll get the same service at the same price and the Treasury will then absorb the revenues. Whether further investment comes is a political choice for Labour, if they don't do it then it's unlikely that things will change much.
They're going to fix the leaking station roof by changing the manager of the station.