Amtrak really needs to enforce the 10 ride, monthly, Metrolink monthly pass riders. ESPECIALLY Metrolink monthly pass holders. Why should someone who pays for an Amtrak ticket, which is significantly higher in cost, have to stand because of commuter fare riders. I personally, think when they give out the seat checks, they add some sort of mark on the seat checks, and have them stand when there are no seats for Amtrak ticket holders.
I believe the policy mentioned was for reserved trains, but where one can still ride on a multi-ride ticket such as a monthly without having to reserve for a specific train. I've looked it up, and it is possible to get 10-ride tickets for endpoints that are only served by trains like the San Joaquin, which is always reserved. The Downeaster is described as a "reserved service", but the caveat they give is that "Multi-Ride Passes are valid for unreserved coach travel only".
http://www.amtrakdowneaster.com/tickets
http://www.amtrakdowneaster.com/multi-ride-passes
I'd be surprised if there's any policy distinction between ticket types for any unreserved coach. And where would your proposal stop? Maybe a priority schedule based on price? 1) Flexible 2) Value 3) AAA/NARP discounts 4) multi-ride 5) Shared service (like Metrolink's Rail 2 Rail or COASTER) 6) Child/senior 7) Fare specials 8) AGR redemptions.
Heck - COASTER seems to have one heck of a deal too. I looked up SAN-OSD and it's $18 on the Surfliner, but COASTER charges this as a 3-zone for $5.50, which the Surfliner will accept for 3 specific trains in each direction. Seems like a good deal to me.
However, there is nothing I can find in Amtrak's policies that states that passes or Metrolink pass holders have lower priority for seats on the Surfliner. Nothing on Metrolink's website and nothing in Amtrak's unreserved train policy that sets a distinction.
http://www.amtrak.com/onboard-the-train-seating-accommodations
Unless specific seats are assigned, seating is on a first-come, first-served basis. On unreserved trains, there are no guaranteed seats.