UK and France seemed to have a few engineering projects like this(cool but not economical), I've seen the channel tunnel described slightly similar.
Already in the second year of its operation there was severe fire requiring a closure for 7 months. Remember Twin Towers or Nord Stream. It's a risky project. I don't want to speculate whether it will still be operated in a century, but a lot can go wrong before that.
2023: Revenue of 1.8bn, EBITDA of 979mn, FCF 638m, 1.5bn in cash. They'll be fine. They're not going to be challenging Nvidia any time soon, but they actually look financially healthy enough for a transport company.
> With Brexit things are unlikely to improve
Interestingly, they may be a rare Brexit beneficiary; their goods traffic seems to be down (as you'd expect) but their tourism traffic is up quite a lot, I suspect because Brexit has made airports more of a pain for British tourists, so taking the train probably looks relatively more attractive. Their revenue is up somewhat now on 2019 (the last non-Brexit-y/pandemic-y year).
> Already in the second year of its operation there was severe fire requiring a closure for 7 months.
Even if it has a major accident, it'll be repaired. For instance see Mount Blanc. Repairing a tunnel, even a badly damaged one, is far, far cheaper than building a new one.
Like I think there's a strong argument that the current extreme consolidation of the industry is quite a bad thing.