I'd assume the Original Lemmings sets alone would be use for the Lemmings remake, and the ONML sets for the ONML re-make. I think.
Anyways, another thing I'd like to address is graphics set distribution. Remember how original Lemmings had somewhat of a lack of crystal style levels? I would assume the set we make would want to be slightly more balanced, set-wise.
Which yields another problem. As an example, if I were to contribute levels, ALL of them would be straight piece sets (In other words, no dirt levels) -- I imagine this would be more a problem with ONML, where I'd be submitting little else but brick style levels. Maybe each author could specialize in certain style-types, and pool together to make levels with the more underrepresented types?
Just an idea. And I'm all for not including glitch levels in the set, for the reasons stated above.