Expansion v. longer trains? There can be a whole dissertation on all the various items needed. The only way to get all these items is a congressional commitment for 10 - 15 years for funding, acquiring additional equipment, requirements for RR acceptance of additional service, majority + RR funds for eliminating repeat locations delaying passenger trains.
An on-time service with reasonable schedules without much make up schedule padding, not retiring or scrapping but letting aging cars trickle down for new routes, heavy demand days ( holidays ), surge fleet(s), charters. etc. All congressionally mandated.
Likely to happen? Not likely. However, that is what we as persons wanting more service needs to advocate and strive for.