I really dig the idea, but I wish it generated unambiguous puzzles. My very first game had a point where it was a 50/50 guess. I mean, maybe it wasn't with solves that were offscreen and came back, but there was nothing I could do with what I was given.
Cool nonetheless, though!
I know the algorithm Simon Tatham's version uses is hyperlocal (it never requires more than a distance of 2 deduction), and given the way the screen scrolls the bottom row will always have at least two rows above it fully visible, so I actually don't think it'd take any modification at all.
In any event, thanks for replying. This really is a neat idea and game. :)