The train could be any of the three categories at points along its route. So it could be classified offpeak for the early part of the journey, peak for the bit through Bristol, etc. It would be easy to show this in printed timetables using the colour coding as I suggest. You would just look at the timetable, and if the journey you were making didn't include any of the peak bits your off-peak ticket would be valid. If it did include any of the peak bits you'd have to have a more expensive ticket.
That might sound slightly complicated but from the passenger's point of view it is a lot less complicated than trying to look up validity codes and so on. And you could still look up journeys on NRE etc just the same as now.
That sounds very complicated! I would argue that validity codes should be simpler in many cases and more readily available (printed on the back of the ticket)?
Most of the off-peak journeys I make have very simple validity codes so knowing my journey is valid to depart station x on any train after time y is simple (or not to catch a train due to arrive at station a before time t). If I then change onto another train on the way which may or may not be a peak train and I'll have to check the timetable for each one sounds complicated to me.
I suspect it would also allow finer control over shifting passengers from busy to quiet services than is possible at the moment.
Anyone who only ever does straightforward return journeys would pay a little more, but most people do a mixture of journey types.
I often do journeys that involve several legs that don't fit neatly into an any permitted return. For example, last christmas/new year I did this:
London to Inverness
Mallaig to Glasgow
Glasgow to Brighton
Brighton to London
I'd say you're unusual if you do things like that often. I'm unusual in buying 2 single tickets a week, usually SON-LDS and LDS-KEI because there is no period return on that flow. I'd presumably gain on that system but the train is full of people going to Leeds and returning the same day, buying a day return. You'll gain though.
I ended up doing this with a mixture of returns and singles, including some returns which I only used part of in one direction. This was because this made it cheaper than doing everything as singles. It is a pain having to waste time fiddling around to find a combination that works, plus restrictions associated with different tickets restrict flexibility. For example, I might have like to make the stop in Glasgow on the way up, but did it on the way back because otherwise it would have been a break of journey on the outward leg of a return. I would much rather be able to buy them all as single journeys without having to worry about whether there's a cheaper way of doing with more complicated arangements.
So you also want to change when Break of Journey is available? If you make that more widely available then more passengers may be able to make a multistop trip on one ticket. Great for them, but potentially reducing the income for the TOC who will have to increase fares if this "simplification" is to be revenue neutral. Again the number of broken journeys is a minority - so you'll gain at other people's expense (again).
Advances could still be sold as they are now, alongside my 3 levels. I think there might be an argument for getting rid of advances too, but that's another (complicated) discussion.
It is indeed. You'd price an awful lot of people out of leisure travel without advances without any obvious benefit for the TOCs.
If I can get a cheap train in advance for £20 more than the coach I may well do that for the additional comfort/speed (where applicable). If the train decides not to compete for those passengers and charges £60 more whenever you book they'll probably lose me for that journey.