64 bit addressing mostly allows a larger embark area.
Huh?
Yes, it would allow this, but I've never seen a single person ever complain about not being able to embark large enough. 16x16 embark tiles = 146 acres! And for the vast majority of people, they're already processor-limited in simulating it long before that anyway, even if they have 64 bit systems, so it wouldn't matter if they wanted more in the first place.
(I have seen many requests, on the flip side, for native support for 1x1 embarks!)
What would 64 bit actually practically do for the huge majority of players of DF?
16x16 embarks come dangerously close to the standard memory limit, and on some worlds will crash. I've had that happen.
Now I agree there is no reason to do a 16x16 embark, you don't need that much space or resources and its just a huge drain on your FPS. Still, most memory issues can be fixed by being LAA.
I agree, we don't really gain anything by being 64-bit. And the conversion to 64-bit shouldn't cause any problems unless he's doing some weird things with memory, which (as a C++ guy [don't hate me]) is awful design 90% of the time (and awesome code 10% of the time).
As to the state of the code-base, Toady isn't a programmer by trade, he's a home-brew, self-taught programmer. When this project started his code probably wasn't very good, and although he's learned, supporting a long lived project filled with placeholders because there was never a complete design is simply awful. Its safe to say the code is probably pretty awful. Of course he doesn't need to make it readable to other people, but he does need it to be readable to himself, if you've ever worked on a long project, stumbled on an old piece of code, and claim to always know exactly what it does you're either lying, or comment too much. It just makes DF more of an amazing feat.