Now, the fact they skipped working on the UX until now allowed Tarn to implement very difficult crazy features Z-level fortress layers and Fluid Dynamics.
Not sure how seriously this was meant, but I unironically agree. I learned, while still in college, never to mock up a "working" polished UI lacking all the complex backend, just to show the client how it'll look when it's done. To the non-computerati, the metaphor is a tradesman working on renovations. If you don't make development versions look and feel like crap, the normies won't accept that it's not "almost ready".
Tarn's priorities here drive away most people, and filters for the sort of person who thinks "modern graphics library" means "ncurses".
Underground river -> Chasms -> Magma -> Bad Things(tm)
The real trouble I had with the old versions was the inability to build walls. As I recall, once you dug something out it was dug forever.
I don't know the minimum off hand but it is probably around 6 normal stone or cave levels, minus the levels used for open sky space and magma sea which I don't know the minimum for. Trees are multilevel now and I don't know that they will grow on a single layer.
All these fixed elements gave the game a specific progression of increasing rewards and challenges, and a guaranteed story arc for the whole fortress.
And how did you come up with that 50 million USD number? Is it multiplayer? Can a major corporation use it to target a young audience demographic? Will there be a mobile version or micro transactions?
If Dwarf Fortress was able to be more than an inspiration and took the "we're selling it" instead which then would allow a different cycle time on features with different priorities, a 50M number isn't unreasonable at all for what the game would be worth today.