Looks like you're right. I did a bit of reading on the reddit and played a little more, looks like it's a fail-state only ending. I dislike it when mods do that, there should always be a way of beating it, even if it is almost impossible. Having a hard fail always bugs me.
The GUI gimmick is building railway infrastructure in provinces/regions that you conquer.
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Completion of each level of railway grants you a number of civs, mils, supply hubs, infrastructure, dockyards etc. It also unlocks new focuses.
For example, getting the rail line up to level 1 in 2 provinces allows you to begin integration of some states.
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The minigame itself doesn't require the player to do anything other than select a target to build in, so it's not like one of those awful Kaiserreich card games where you have to watch it like a hawk. It also only needs a small amount of PP to offset some of the poverty effects so it's not a blackhole of resources. It does stop you from manually building rail lines, but you get these and supply hubs from the mini-game itself and I never ran into a problem with supply. The only time where a player will need to build rail lines there is a focus that unlocks the option for an in-game year. It all works really well.
It's hard to accurately describe it with words and screenshots, but it plays really well and just fits the overall flow of the nation. It's what a GUI gimmick should be; it adds to the gameplay rather than being a substitute for gameplay.