First class being a different "goods" type would address this: there would pax routes (with the "best" winning) and first_class routes (with the best winning), just as mail and pax can and often have different routes. The only drawback would be that first_class would need to be handled separately from origin to destination, hence having also dedicated feeder lines (e.g. taxis).
Talking of good types, it would be nice to have 4 types of "goods".
- pax: transport building to building
- ware: transport factory to factory
- waste: transport building to factory
- delivery: transport factory to buildings
Each pakset-defined good should belong to one of these types.
E.g.
pax, first_class, and mail: pax
iron, coal, books, oil, gasoline, etc...: ware
garbage: waste (collection door to door)
groceries, newspapers: delivery (delivery door to door).
Production rates of wares would be factory-defined and wouldn't change present behavior.
Generation rates of pax-like would depend on building level, with different rates according to res, com, and ind building type (current behavior, but additional pax-like would require new pakset-defined rates)
Production rates of waste-like goods would be similar to pax generation, with additional rates.
Production of delivery goods would be factory-defined, similar to wares.
Stations could have selective storage, e.g.: enables=pax,first_class,mail
This would give paksets greater customization, from present behavior to extremely complex goods types.