Even then, I believe the ADA still requires that all stations have to become accessible at some point.
So, I know this stuff. The ADA doesn't *technically* require that, but it does in practice. The ADA requires that any station which is *renovated* become accessible during renovation. (There are some super-nitpicky exceptions which almost never apply.) And also all new stations must be accessible. The belief was that this would, eventually, make all stations accessible, because you can't leave any station unrenovated forever -- it'll crumble away!
And indeed this has largely been how it has worked for most systems. A station needs some repairs, it has to be brought up to code and made ADA compliant -- so there are a lot of non-"key" stations which are accessible in every legacy urban and commuter rail system. They're all getting more and more compliant over time.
Do you (a transit agency) have crumbling stairs and a dangerous platform, and are losing million-dollar lawsuits over people falling and injuring themselves? In order to fix the stairs and platform, you have to make the station ADA-compliant. This is how a bunch of Metra stations became ADA-accessible.
NYC Subway flagrantly broke this provision of the law repeatedly, renovating stations for millions of dollars without making them accessible. LIRR and Metro-North, also MTA subsidiaries, also violated this legal provision. They all lost a bunch of legal cases over it. Everyone else complied with it.
Amtrak... well, I think maybe the reason Amtrak was required explicitly to make all stations accessible was that someone in Congress realized that Amtrak was quite capable of not renovating a station for 50 years plus.
For Amtrak, the renovation rule is actually older than the ADA: the rule has been in effect for Amtrak since Amtrak was created, thanks to the Architectural Barriers Act of 1968 which requires that any train station (or other public building) renovated using federal funds be accessible. Amtrak's history of substandard unrenovated stations was something Congress was well aware of in 1990.
Amtrak has their major transfer points already accessible, so yes, it's time for Amtrak to get everything up to snuff (that time was 20-30 years ago, imo, but now is better than later.) Same with CTA, MTA, etc. - eventually all stations should be upgraded to meet ADA standards - and have those accommodations be reliable enough that they can be counted on 24/7/365.
CTA has a plan to make all stations accessible. Boston MBTA has a plan to make all stations accessible. Philadelphia is working on a plan. These are agencies with *difficult* station work. (Philadelphia's City Hall station alone is well over half a billion dollars. MBTA Green Line surface stations are in the middle of narrow street medians and require agreement from the city which owns the roads to widen the platforms to acceptable-for-wheelchairs width by removing car lane space. Boylston is a historic landmark and requires a ton of paperwork to alter. All of them have underground stations which are expensive to alter.)
They all provide annual status reports on their accessibility projects progress, and respond to "what's the holdup with making station X accessible" questions. Cleveland RTA has always suffered with even less money to work with than Amtrak, and *they* have been issuing reports on their accessibility progress (and managed to meet the legal deadlines).
Amtrak mostly has *easy* stations left -- the least they can do is to provide the annual report on progress required by the settlement with the DOJ. I mean, I can imagine that there are genuine reasons why Harper's Ferry work is delayed (being a national park and historic site) but I don't actually have any information as to why it's delayed. For the Keystone line stations it's even less excusable.