As part of my only self made thread here on this forum, (likely dismissed because of the thread starting with me griping about how time works in the game and/or stuff already being brought up in the past) I suggested the addition of "geologist" Dwarfs who have honed there innate "stonesense" such that they can survey areas and get a good grasp of exactly what is in an area and how best to attack it. When it comes to mining skill, Toady needs to either drop it, or decide how he's going to have cave-ins, seismic activity and other elements evolve over time. Anyone can dig a whole, it takes skill, talent, and experience to stop the ceiling from filling the new void.
What this ends up meaning will assuage some fears about full AI tunnelers while creating new, connected ones. In order for mining skill to be relevant mining must be inherently dangerous as it very well should be. This means chances of cave-ins, running into things that are already living there, having miners not now better than to dig into damp/warm stone initially, ect. Mining would need to be broken into multiple skills and even labors with some Dwarfs digging while other shore-up the walls and ceiling. Supports, and space for them, would be
mandatory, no more simply using then for traps and what not. The use a single tile to hold up a massive structure trick? Dead. Building mega projects without regard for the full range of physics? Dead. Of course this means that it will take those Goblin hordes a while to tunnel to your fort's interior since they are only slightly smarter than Gully Dwarves(
http://en.wikipedia.org/wiki/List_of_Dragonlance_creatures), and Goblin sappers have always been a fantasy genre running gag more than anything.
It's a tough pill I know, but this is the future of DF.