Jesus, what is wrong with people...
If such a thing were to happen, it would be cool, and have absolutely zero impact on DF players. But you're so far up your own ass that you can't stand the idea of someone having fun in a different way than you?
Minecraft is very cool, its giant worlds and tons of crafting options are tons of fun for a lot of people, as evidenced by the very fact that people are willing to pay for it, and if the creator of an indie game has managed to make lots of money off it, good for him.
If you don't like it, don't play it. If minecraft is low quality, what exactly is good quality, in your opinion? Does it just piss you off that it can be played multiplayer, and has 3D graphics, which are SO mainstream.
I used to play it quite a bit, and then I got bored. Just like DF. Just like every game ever. When a new version of DF comes out, I'll play it again. Same for minecraft. Can't there just be two different things which are both good, for different reasons? If I could have a cool world in DF, then import it to minecraft, that'd be pretty neat.
/Rant
I would think a DF to MC conversion would require at least a 2x2 MC tile for each DF tile, since DF has a seperate floor and wall layer per tile, as well as making an up/down staircase usable. Most DF stone types would convert to MC stone. Ores would either convert to an equivalent ore, or into stone. Same with gems.
Really, it doesn't seem like there's any overriding technical issue why it couldn't be done.