Amtrak offer no reservations on trains taking over 48 hours!
Amtrak don't allow reservation of specific seats on a lot of trains, but they do stop selling tickets when they've sold enough to fill all of them. They don't have flexible tickets.
That's what I would like rail to be, but I suspect that many people would prefer a French style system where they can use the train when they are able to plan well ahead, knowing that they'll get a seat and won't find the train full of standing passengers, and when that doesn't work for them they'll just drive.
And if they can fill their trains like that, that probably works well for the railway too.
One thing I've noticed with this post COVID fake compulsory reservations nonsense is that the majority of people will complain about overcrowding and secondarily high fares (though with them already being perceived as high, a bit higher doesn't seem to have much effect) they seem to accept "sold out" as just one of those things, given that most other things where you have a seat (coaches, planes, cinemas, theatres etc) can sell out and once it does it's tough.
As I said, it's not my preference. But I do wonder if we might be nearing the point where the majority of people would indeed actually prefer a French style approach for long distance travel.
If due to age or state of health not getting a seat is a big issue, it's something that puts people off rail.
I'm 6' 4", I'm not afraid of telling someone to get out of my seat and doing something like moving their bag if they refuse.
I suspect my Mum wouldn't, and it seems clear staff aren't willing to do it either for fear of assault. "I'll get the guard" is no longer a threat; the guard won't do anything in 99% of cases. Only if RPIs are on board is anything likely to be done. The passive way to deal with the problem is to ensure everyone has a reserved seat and a seat selector is present, then there's no reason to prefer to sit in someone else's. I know the 70 minute thing means this isn't absolute, but it would certainly be quite different from say GWR where Advances are generally poor value and so a lot of people are on walk-ups just because they were cheapest.
I'm not sure that due to these issues I don't lean towards the idea that reservations should either be compulsory or non-existent on any given train and that optional doesn't work well - but that's very much one for another thread!