How would it work with season tickets? Would it eat into that revenue?
Presumably it wouldn't change them and passengers would just have to decide whether the season ticket 'discount' is worth it or not. Anyway, it seems unlikely to happen.
The original poster didn't really explain why they were advocating fares being set at off-peak levels throughout Friday, other than noting that Friday morning demand is lower than other days of the week.
The use cases appear to be:
* To encourage commuters to travel on Fridays instead of other days of the week. Some people appear to take the view that it isn't worth coming into a workplace on a Friday, even though they attend on other days of the week. The theory of those advocating off-peak fares on a Friday is that some passengers would be encouraged to use the railway to get to work on Friday, instead of another day in the week, spreading out passenger loadings.
Where this one appears to fall down is that it isn't at all clear that cheaper fares on a Friday will change this behaviour. If there was a switch of days, then the railway makes less money, but doesn't have to worry about making more capacity available on another day of the week. If more passengers travel on Friday, the railway has to consider whether the extra travel makes up revenue from the loss of revenue from those who had to travel anyway.
This didn't appear to work in the TfL trial, as TfL reported an overall revenue loss from its off-peak Friday trial earlier this year.
* To recognise that there is spare capacity such that it could be used for leisure travel, potentially switching travel from the Saturday morning "peak". However, as already discussed, the reasons to travel early on a Friday, instead of later in the morning, or on Saturday, are quite niche, and it isn't clear that the revenue gained by helping leisure users save some costs on Friday morning exceed the reduction in revenue from other users of the railway. To some extent, this can be done with advance fares in any case, without needing to change the terms of off-peak tickets, particularly given the apparent direction of ticketing for long-distance travel.
While there may be some people who don't work on Fridays, for whom this would improve their access to leisure travel, it seems fairly unlikely that people working Monday to Friday would take annual leave to use the railway in a big way early on Friday mornings, because the level of leisure activities available on a Friday, rather than Saturday are more limited.