How accurately do you plan to make the map rewrite simulate geology? The 3 yards to one vertical block scale would make it unlikely for dwarves to get to magma, so I'm assuming not that accurately, but can we expect to see proper geological folds and igneous intrusions, with accompanying rock types, as well as the sorts of structures on the surface that one would expect to see due to erosion? How about glacial deposits? Would geological ages be included in the pre w.g. myth stage?
I just wanted to note that the current setup is less "doesn't simulate Earth geology well enough" than "fantasy setting doesn't run by the same physical laws". The best available info is that the DF world is a more or less artificial construct of fairly recent age (certainly by geological standards); approximately designed to look similar to a natural planet on the surface by the god(s) or meta-godlike entities that created it. The whole question of why / how the world appears to a thin shell of rock over a slade (scrith) foundation perilously suspended over (or floating on) an infinite pit of demons and hellfire is troubling at various levels if you think about it much.
Among other things, there is no current in-game evidence of subduction, sea-floor spreading centers, or even such Victorian ideas as planetary cooling crustal shrinkage. The topology is created in an initial state, gets a few volcanic hot-spots punched through, gets eroded a bit depending on settings and local rainfall, and that's what you end up with. The DF world may well be a temporary stop-gap by the god(s), and as presented would fall victim to the erosional problems of classical steady-state
Regarding glacial deposits, some of the sedimentary layer arrangements found in the lowlands can be interpreted as such, although there is no specific mechanism for large-scale glaciation (or any other non-steady-state major changes).
In any case, the upcoming Myth arc will radically change the way the worlds work; one of the examples from the talk was "fragments of the Cosmic Egg", and various other popular takes like "a disk supported on the back of seven giant olms" are likely to come up. The "geology", if one can even call it such, of such fantasy worlds is likely to be even less Earth-like, and ideally strongly connected to the myths of the world's creation at all but the lowest-magic levels.
That said, I'd love more interesting geology, realistic or otherwise. Intrusions / dykes, 3D ore veins, and so on would be a real improvement that would be useful in a variety of world systems.