Everyone is jumping in to disagree with the OP. I have to be honest: I thought the OP's points were very well made, and as much as I loved the LightTable demo, I think I immediately dismissed it, in my mind, as "looks cool, but can't be made". I think there is a big disconnect between this author, a "working programmer" who actually writes code, and at least some of the commenters in this thread. Let me give my take…
Why not? It's definitely cool and definitely can be made. The question is: will anyone want to use it, or is it just cool? Is the learning curve too steep to make us want to adopt it as our primary text editor? Does it really confer efficiency advantages over Emacs/Vim/TextMate/XCode/Eclipse/etc?
To me, it stands a good chance of being widely adopted if and only if it is actually more efficient to use it and if the time of adoption doesn't outweigh those efficiency advantages. I don't have an answer to this question, because I haven't actually used it. I suggest that since everyone else hasn't either, we wait to pass judgment on whether it will work or not.