... For basically its entire existence--nearly 20 years--DF has been a very very gritty and low fantasy game. ...
Warning: mild spoilers for endgame stuff
I would disagree with this. A significant part of DF from very early on (well before it was 3D) has been the magical "geology", the immortal elves and goblins, and in particular the demons. The whole world is literally infused with magic; the dwarves' ability to tunnel through granite with copper picks at ludicrous speeds, carry objects such as stone floodgates around, turn three gems into an entire window-wall, have underground roads connecting cities across entire continents, routinely work with exotic fantasy materials such as adamantine, and of course construct all sorts of nigh-impossible things while in a strange mood.
Plus the fact that if you dig only a few hundred feet down, pretty much anywhere in the entire world, you encounter a massive, continent-spanning network of elaborate caves, full of fantastic creatures, exotic fungal trees, animal people civilizations, and deadly horrors from before the dawn of time. That doesn't even begin to get into the "new fun stuff", with the "geodes" surrounded by impossible collections of jewels, that can contain magma mysteriously kept hot without any exterior connection or reason, demons, and actual angels fully decked out with exotic materials with no match in mundane reality. Then there's the fact that the entire inner structure of the world is based on what appears to be unlimited, universal hell lurking barely below the surface; mystical people sometimes talk about the "thin veneer of mundane reality", but in DF, that's an all to literal description.
Is it *possible*, with modding and some care, to play a low-magic, low-fantasy "Human Town" that gets by on the surface and doesn't interact with the intensely magical world? Yes, but that's not the default or core DF experience.
The best fantasy and science fiction take a fairly small set of assumptions about what makes that world different, and then logically expand out from there. DF is not "low fantasy", but it makes a credible attempt at "hard fantasy", a rarely-encountered term or genre.
All that said, however... it's been discussed several times that when Myth & Magic comes along there will be at least one, and possibly a whole slew, of world-gen controls to set how fantastic the world is; from nearly mundane to the extent that the DF simulation can support it, to much crazier than the current DF. It is highly likely that one (set) of the settings will be intended to more or less replicate the current level of DF, possibly with some hard-coded presets that can be turned on or off.