I mean its fairly obvious that passengers will lose flexibility here. I absolutely get that most people don't use that flexibility (hell a lot of people don't even know it exists), but it will be lost. I will no longer be able to buy a Bath to Cardiff anytime return, use the outbound normally, and on the return stop off in Bristol for a couple of days (example from a few years ago when I did live in Bath).
Yes, I agree that that specific piece of flexibility would be lost. However, it's used by a tiny number of people, and out of those people the number who would do such a break unplanned (so couldn't do it by rebooking) is even smaller to the point that I reckon it'll be in single figures or maybe tens per year across the entire rail network*. Thus, it can be substituted for by splitting at the desired overnight break point. Sometimes this might cost more but sometimes it costs less! (Were this not the case Trainsplit wouldn't be a thing).
The majority of break of journey is same-day, i.e. to stop off for a meal because you're hungry, for example. There's no real reason bar "restrictions anomalies" (that just need fixing) why all tickets shouldn't permit that, even Advances provided you use the booked trains.
* I suspect those who do do unplanned overnight breaks of journey are almost all young university aged rail enthusiasts, a group which is proportionately overrepresented here, who might randomly decide to visit a friend, get drunk with them and stay over. Almost no older adult with a family is ever in a position to do this even if they wanted to. Thus I think we see more protest about this here than in the general public. I've, that I recall, done it once ever, and I was about 25 when I did it!
But it would be a fare rise which is the point I was making. We can't all sit here and pretend these changes aren't going to mean some people end up paying significantly more!
You can't make an omelette without breaking eggs. The fact that some won't accept this is one key reason we've ended up stuck with an unfit-for-purpose system. People here love the current system because they're skilled at gaming it, but a system that can be gamed to the extent it can is by definition a bad one.
As a passenger, the way I see it is the 100% of a return thing is simply because a 2 hour delay on a journey has a massive impact on the passenger and likely significantly messes up their plans, and so is almost an apology to make sure they aren't put off travelling by rail in the future! As for them being rare - granted but I have still had a fair few of those in my time!
It just seems a cack-handed way of working it out because it only compensates some people depending what ticket they've bought. If it's justified to compensate more, then make that 120% of the single, or something. Or make it a full refund plus a free ticket or something.
But it is that "maybe fractionally more" that a lot of us are concerned about.
For users of Super Off Peaks it isn't "fractionally more" on the LNER trial, it's exactly the same. The Off Peak was lost, but it was applicable to only a small number of journeys, some of those can be done with an Anytime Single plus a Super Off Peak Single for about the same money. Some of them might involve an Advance, but I doubt many people ended up paying much if any more. Some may even have found a cheaper way but just bought that ticket by default. Or some might have found they could buy a Super Off Peak out and then bought the return when they knew when they were going to travel, adding further flexibility.
You can't make an omelette without breaking eggs, so SOMEONE will lose out, somewhere, we just have to accept this as it's impossible to change the system without that (remember, if we add subsidy the taxpayer loses out, and most of us are taxpayers). But many will benefit too.