How far away, tentatively, is adventurer-enabled mining and constructing?
As usual, unless the feature is directly mentioned in the upcoming releases, nobody can give you a meaningful answer for when it'll be implemented, not even Toady. It could sneak into release 2, 7, or 9, or it might be even later. Releases will probably each take at least a month. So, I would guess between one month and one year from now.
I was rather interested in an in-engine evaluation rather than time, I know it won't be around the bend for a while. Such as, what are the biggest things in the way at the moment. I can guess handling the random small sites is one such thing, since the actual mechanics already exist in Fortress mode.
Oh, and a related question.
What is your opinion on a possibility of a waypoint/target-based Adventure mode control system? By this I mean that you would control your adventurer like an AI unit, and the game would use its own pathing engine to move him. For lack of a better comparison, think Diablo. Click/point to a destination, the character walks there. Select an enemy, the character attacks. All done in realtime with autopause, preventing, for example, horrendous control problems from control lag in large cities. This system would also, essentially, allow using Fort mode tasks and constructions more or less as-is. Manual direction-based control would be preserved, of course, to handle situations that the game's pathfinding can't, like jumping, flying, or swimming.