At this rate, I'd be surprised if it's up and running before 2022...
If we ever do see the first extension to Sheffield's Supertram in over twenty years then it could be truly transformational for a number of "marginal" routes that currently have heavy rail and all of the costs (infrastructure, signalling etc) that this requires.
If Tram Train happens in South Yorkshire then it could be a way of transforming lots of branch lines, a more flexible type of vehicle that could extend into town centres (rather than a current train station that was well located in Victorian days but now some distance from where people want to go), it could allow local control over services (since they wouldn't have to be run by TOCs), it could revitalise a lot of ignored lines. But it keeps getting pushed backwards and backwards, and doesn't seem to be a priority for anyone.
Other things:
A resolution to the DOO issues currently affecting a number of franchises. Will there be a domino effect or will the Unions win?
Devolved power in England - how will the different flavours of devolution offered to different areas affect railways... how will the different areas interact (e.g. will there be the kind of squabbling we've seen with the Wales & Borders franchise?).
The seats on new stock won't be comfortable enough for enthusiasts.
If the GA franchise is anything to go by, will we see new awards ditching their BR-era trains to go for cheaper/ more efficient modern stock? That could lead to a bit of a cycle of dumping older trains but also a new wave of micro-fleets (just when you thought that everything was going to look like a 377...)
Oh, and by 2022, Jeremy Corbyn will finally have found a seat
