Dwarf Fortress is a wonder of content generalisation in gaming, so it does seem very odd that it runs on a tile based system.
Using rudimentary meshes instead would open up so many possibilities!
Obviously, the game would be confusing and unfamiliar if it abandoned the tile system together, but it's easy enough to have it so that designations are still tile based, and tiles render based on what meshes are inside them.
Here are the things that I think become better:
-Creature behaviour becomes much more realistic, as diagonal and orthagonal movement can be made perfectly identical in terms of real distance travelled, and by giving each creature a particular position with a tile it's no longer possible to have a dozen attackers standing in one tile. With animation of creature meshes, it becomes possible to make more accurate calculations of hits in combat; so it won't be so easy to kick a standing person in the face anymore, and if you aim for someone's fourth right finger and miss you might hit something else.
-Multi-tile creatures and constructions will handle their own visual appearance, they only require meshes (Which mostly exist already) and animations.
-Mechanical stress to constructions and natural structures become possibly easier to calculate as terrain shapes can be simplified; not to mention that meshes can collapse in swinging motions as well as straight down.
-Open space can be extended enormously without hitting performance.
-Adds the possibility of dropping tile rendering altogether, which modders would really like.
-Gases such as mist and miasma no longer have to be so taxing to simulate, they can be replaced with moving points that say "at distance x from me, the density of gas y is z".
The things that would become harder would be pathfinding and water flow, but if they were made to work they would be better than they were before; the currently clear-cut definition of what movements are trivial for a dwarf and which are difficult would become blurred, so the game has to be programmed so that a dwarf will consider leaping and climbing outside of combat; as for water flow, the amount of simulation required could end up decreasing for large volumes, and simulating objects in the water being pushed by the flow could become more realistic (an object no longer has to be pushed a whole tile suddenly to be pushed by water).
Adventurer mode would probably become weird and difficult though, since only AI creatures would be able to see and navigate the mesh-based world.
Thoughts? Accusations of heresy?