Most of the OP is meandering hot air fluff (2d nostalgia? Really? And complaining about different colored stones? ...), but I resonate with two main points strongly.
I understand these two things aren't fun to do, but regardless, prior to any other features being developed IMHO,
1) The game needs Needs NEEDS to make its GUI modular and separate from all underlying code. The game needs to send information about each tile and what exists there in an information format API to the generic, abstract GUI, so that we can all go and make whatever graphics we want without getting in Toady's way. This is #1 priority, IMO. (He can keep using ASCII and not worry about it after that!!)
2) Less of a priority, but still I think more important than any given feature... As close as possible to every single constant number and string in the code should be moved to the RAWs. Basically anything other than math functions and abstract frameworks. Every building, every reaction, every script of code for one-off things should be tagged to be able to be used elsewhere optionally. Everything from gravitational constants to internal scalar values in the worldgen code. Because every minute Toady spends coding things into RAWs unlocks hours of time that the community modders can spend making millions of diverse features to keep players entertained. It's like investing in a highway system instead of investing in horse drawn carriage subsidies. It's just always going to be stupidly more efficient at contributing to game epic-ness than direct, solo, lone wolf coding by Toady while other people sit around twiddling thumbs or banging their heads against the wall finding absurd roundabout workarounds.
(Basically, if at any point in the code it says "X = [some specific number other than pi]" or "Z = [some specific string other than Toady's name]" and they aren't pointers to the RAWs, IMO it's doing it wrong.)
And then when there isn't much else to put in the raws, and the GUI is out there available to be made 50x more epic, THEN it becomes more efficient to go back to adding new features.