Okay, this is a VERY rough idea at the moment which may have been done in the past, but I think it could have legs with the right tailoring.
In the Original version of Lemmings, there were quite a few levels (about 35, I think) which had no repeats. Most of them were from the harder two difficulties, but there were a few easier levels which didn't have a repeat. I suggest trying to create repeats of these levels which either increase difficulty, or completely change its solution. Of course, some levels will be harder to do than others, but still, I like a challenge.
Take a running jump, And then there were four, and Tailor-made for blockers instantly spring to mind for me, but, of course, there are loads to pick from.
So, what do you think? Good idea? Bad idea? "Shut up, Adam!"?