I have subsequently done the end of the railway and, as of today, the end of Evolution.
The Railway is quite a good part of the game, albeit one which suffers a little from FL's late game grind tendencies. The Tracklayers' City section at the end is an interestingly weird but very Fallen London way to end the story, and the mysterious... antagonist I think is the wrong term, perhaps just "obstacle", is a genuinely fascinating enigma. You pick up a lot of new locations with their own side-stories along the way, each of which is very different and some of which open up a lot of new opportunities elsewhere. That's all great, but it can sometimes be tricky to keep track of, especially with FL's huge proliferation of item types and, at times, lack of clarity in how to find and use them. I do think it's a good part of the game, anyhow, but it's a slow and very large thing to explore and whilst it has some overarching plot elements, they're a little sparse except a few big moments later in the sequence. I'm looking forward to seeing what Tracklayers' City content evolves in future, though the TLC does seem like it's a bit of a wish-fulfillment of "Fallen London is big and horrible, what if you could just build Nice Socialism Town according to your personal ideological preferences?" But that said, I'm not going to turn down that chance if offered it.
Meanwhile Evolution is a really nice story and one of my favourite of the big late-game content sections, in part because it's a pretty clear and effective narrative and in part because it isn't too grind-y. It might have been worse if I'd completed it earlier, as I think you may be meant to do, but there are few really big resource grinds involved which means the story continues at a good pace. There are also some of the best narrative moments I've hit in Fallen London in there: the game manages to make the dive (and I won't say more about it than that) very atmospheric, and some of the confrontations are genuinely well done with an effectively thoughtful adventure-horror that fascinates and appalls rather than just sickens. The end could maybe have done with a little more oomph, but it was well written and felt earned and the new location available at the end is really interesting.
I don't think I've got much big plot stuff to do now, but I have got a lot to explore which feels a nice state to be in for a patch of reduced occasional poking at Fallen London. I'd like to do more in the Khanate, I've still got some bits to do to tie up loose ends in Evolution, and I've got bits at the later railway stations to tootle along with.