SS will be expanded by 2025. That's not in a lot of doubt. If left in a vacuum to the two federal entities to sort out, USPS will move out and Amtrak will move in. What's the price of inaction from the state? How about Ft. Point never happening and the feds taking the opportunity to consolidate the sorting facility out of existence, scatter it to the winds to other smaller regional facilities or moved out to cheaper digs in the 'burbs, and slash lots and lots and lots of local jobs that'll give Congress a warm-and-fuzzy feeling. Then tincan platform shelters outdoors facing unprotected howling wind off the Channel. All of that can be done rather quite economically at cost of razing more infrastructure than it builds.
The fed interests would be quite happy with that because Amtrak gets its capacity, they get a great excuse to seek the cheapest and most skinflint way to downsize the regional USPS to a bare minimal existence, and they can act free from any obligation to local partnerships or the BRA's sloth. This isn't a long-term threat to either agency's basic infrastructure needs. It's the state that wants to give them shiny things. They just want to run trains and mail delivery on-time. They can get that through other means (and I would argue Amtrak's got the rare upper-hand here comparing long-term revenue trendlines NEC vs. regional snail-mail).
This is a very lower-case version of the perpetually troubled NYC Moynihan Station annex on Penn Station. Amtrak is a partner in that, but they don't have a horse in whether it collapses under its own weight because it doesn't cost them one single schedule slot if their platforms are in a 'landmark' station or not. There are factions inside of Amtrak that would kind of prefer that to happen because it's less congestion they'd get from NJ Transit and MTA commuter trains who'd be main beneficiary. SS sans creature comforts is no different. If they get their platform slots guaranteed the T can expand as little as its heart not-wants.
It's wholly the city's and state's loss if their ineptitude and inflexibility costs them a one-time development bonanza for the city and lots of local jobs over the same. They shit their own bed here. Life and capital improvement planning trudge forward for the quasi-federal corporations. They're too big and far-flung to get their key initiatives upended by a city and local-yokel transit authority that habitually choke on their Meninomonument proposals...and they knew this going in.