The problems I would see are:

- if you book with train company A and they have 5 services a day (which they have bidded for and win) would you be able to switch to a different provider of their services were full?

- a family of 5, with 3 younger children is traveling and they try to book in late to a 390 with 11 coaches, there's 35 seats showing as available, yet there's 3 or 4 in each coach and none very close to each other.

- how will allocating tickets work? Would it be that there's X tickets available a day? If that's the case (the numbers are to make the maths easy) if there's 10 trains with 100 seats (1,000 seats a day) if 500 tickets are sold and the first 6 trains of the day each have 15 people traveling then there's not enough capacity in the remaining 4 trains to seat all 410 people who still have a valid ticket for that day.

- what about if someone isn't able to get a seat between B & D because there's no spare seats between B & C because of someone traveling between A & C, even if they overlap is 10 minutes whilst the overall journey for each person is measured in hours?

I'm not saying that it wouldn't work, but I do think that there's a lot more to think about before it's a workable option.