For the Holiday Lemmings suggestion, why not just have an option of including lemming sprites as part of a style? Then, if no custom ones are found, it reverts to the default ones.
I should be able to throw together something to rip the holiday lemming sprites from H93/H94.
Also, I believe the L2 levels, even classic, are tile-based, unlike L1 which is based on elements at various positions. Therefore, a direct rip would be of no use, unless you expand the formats Lemmini supports; you'd be better off just remaking the levels.