I'd be nice if they could run a service from (say) Birmingham to Stansted Airport overnight (and the other way)...
Currently, here in Peterborough:-
The last trains on the Stansted to Birmingham route leave at roughly the same time (2021 Stansted & 2025 B'ham) and then that's it until (0519 from B'ham & 0516 from Stansted)
Unless of course, you want to travel via London!!!
It's a bit of a trek, if you've got either a early/late flight @ Stansted!!!!
I agree - during the day it is possible for me to get to 3 small to medium airports - Manchester, Liverpool, Birmingham - within an hour's train journey, and to all of the 6 London airports, plus East Midlands, Bristol, Cardiff and maybe a few others within about two to two and a half hours.
But the earliest journey opportunities to most of these mean it isn't feasible to take a flight departing before around 10am. This can severely limit the choice of dates where there are affordable flights, as for example Ryanair run many of their cheapest flights departing at near 7am.
The only option I then have in those circumstances, if I want to take those flights, is to take the coach, which typically means leaving home at a very late hour, making a journey right at the time where I would rather be sleeping, and then arriving at a very early hour. Depending on my luck with the prices, it may be considerably cheaper than the train journey, or at worst approximately the same.
A 24 hour rail service on all of the 4 track mainlines isn't too much to expect in my opinion, even if it were only at a third, or even a quarter, of the frequency the daytime off-peak service. But sadly the earliest trains from my station are around 05:30 and the last ones around 23:00.