If I recall correctly, when the other public sector pay disputes were settled, it was on the basis that there was no increase in budget to the relevant departments. I.e. the money to fund the pay increases had to be found from existing budgets.
This is no different to the railways. The only difference I can see is that what changes will be made or wanted to fund the pay increases are unknown elsewhere, whereas the railways have been given a list of ways where they are expected to save money.
I don't think there is any chance of a speedy resolution after an election if Labour come to power, they will have no more money than the current government and probably, by then, even less if the Tories adopt a Scortched Earth policy. There are far higher priorities in the national discussion such as hospitals and schools, as opposed to railways which aren't that important to most people.
There might be scope for movement now if:
The RMT said that they would end the current dispute and strikes if they were given a one year no strings deal;
They agreed they would accept and agree to some productivity changes in each TOC;
BUT, that these changes had to be discussed and agreed locally depending on the situations in each company and each grade and they are not agreeing at this stage to the specifics of what productivity changes they will agree to.
Such a proposal might well be accepted by both sides and would achieve progress for both sides.
The alternative is the strikes continue, the DfT close most ticket offices anyway, and then once the consultation for that has been concluded they will move on to finding ways to impose the changes they want elsewhere in other grades.