Okay, so I just made a level that I can reveal. :)
"Don't Forget!"
10 lemmings, save 9
RR 60, no time limit
1 Climber, 1 Glider, 1 Bomber, 2 Platformers, 1 Builder, 1 Basher, 1 Digger
(Image attached).
I'll also reveal a couple of very minor details about the final level. Very minor, but for those who might want it to be a complete surprise I'll spoiler tag it anyway.
The graphic set it uses is one of the Lemmings Plus IV ones. The skillset has a total of 26 skills; all of which are (at least currently) given from the start rather than as pickup skills. It's also smaller (but probably much harder) than LPIV or LPV's final levels.