I do kind of equate this to train travel, where it's actually quite common to get off at an intermediate stop between endpoints on a ticket. But that's a different dynamic, where it can be within the rules set. When I used to commute on Amtrak, I'd get what was called a "multi-ride" ticket where I actually bought it for two endpoints that were on the far edges of my possible travel, but where I might travel in between. I might pay a little bit more (or sometimes not) but I would get a bit of flexibility. I remember when a conductor came up to "punch" my ticket (eventually this became virtual, but it was previously a hole punched in a spot on the ticket) I was asked where I wanted to get off, as long as it was any point up to the endpoint of my ticket.
But there was a lot of flexibility. Most of my train travel was considered "unreserved" where theoretically I was on a manifest for a specific train, but I could use my ticket (almost) any time before or after (up to a year after the ticket purchase date) unless there was some sort of time restriction on it. Some routes were considered "reserved" for specific dates around holidays. So not showing up didn't cause any kind of panic. Passengers getting off at intermediate stops for airline travel creates issues with head count. I've heard of the skiplagging/hidden-city passenger resulting in flights being delayed as flight attendants tried to match the head count to the passengers and figure out who got off and whether or not they might have had checked baggage (i.e. worries about explosives or something else) or possibly left behind something that could be dangerous.
And I've done a few things to save money on train travel. I couldn't really do it when I did points bookings, since they weren't subject to normal discounts, although there could be points discount promotions. But one of the things I did once was book with a 20%
Disneyland promotional cash fare discount that required that one of the endpoints was Anaheim. The discount was on the entire fare including any associated bus segment. I did actually board in Anaheim the last time I took the discount, but previously I booked that discount where I ended up boarding in Los Angeles. The full fare is $60 from either Anaheim or LA to Oakland for my specific route.
AMTRAK TERMS AND CONDITIONS:
This offer is valid for 20% off the regular (full) adult rail fare.
********
Travel is valid to Anaheim, CA and return only. This offer is valid for travel on the Pacific Surfliner and associated Thruways; except not valid on the 7000-8999 Thruways.
I have a (PDF) ticket stored and the boilerplate terms say that travel is allowed within the endpoints, but then says that promotions may limit that.
eTickets for Unreserved Coach services are valid within the limits of the city-pair paid for and within one year of purchase, unless otherwise restricted by any special or promotional fare paid. Seats may not be available and you may have to stand.
But Amtrak train travel is really weird because mostly the tickets are checked on board, with the exception of some stations with gates like NY Penn Station. I've been on an Amtrak train where I waited a long time for a conductor to check my ticket, and even where it never got checked (one conductor told me to feel free to reuse such a ticket). I've boarded in Anaheim going north, where my ticket wasn't checked until I got well past Los Angeles, so if they see me with a ticket near (let's say) Ventura, it's hard to know exactly where I boarded. And for the most part they don't care like the airlines do about hidden-city. But yeah I get that I might be running afoul of the rules, but this is one where I doubt there's much that they'll do about it.