@Dexter - that last one (the pillar one) looks incredible, probably the closest thing I've seen to an OG style so far. It almost looks like it could have been one of the vgaspec levels.
My own style creation skills tend towards remixing/tweaking what's already there rather than creating something entirely from scratch; I admire anyone who can work from a completely blank palette. I can do that with music, but even then I tend to use familiar themes and melodies, and like to stick to tried-and-tested instrument groupings/voices.
Anyway, here are some ideas I had whilst I was driving the other day; I thought I'd share them here in case it sparks anyone's artistic engines. Pieuw's comment about the OG styles being a "toolbox to build anything" has been the inspiration here, and seems like it would be a good thing to keep in mind throughout creation of any lemmings style.
Plasticine Factory - the idea here would very much be abstract shapes and blobs, but long thin pipes of plasticine could also work, as long as they taper at the end like plasticine snakes tend to. These could be complemented by more generic "factory / laboratory"-type items like metal/plastic tubes, grilles, etc.
Gold / Treasure - think a mixture of ohno_brick and orig_crystal, but with gold bullion, gold chains, ornamental spindles, coins, and of course jewels and other items. Bonus points if the items aren't too specific, and can be joined together to make larger items.
Glass / Ice - this would be a mixture of spiky, jagged shapes and smooth curves. Use of semi-transparency could make this look quite magical.
Lego - this lends itself very well to the idea of "make anything from this" - it has already been done by Arty, of course, but that doesn't mean we can't revisit the idea and expand on it.
Many of namida's styles also have a lot of potential. Martian, Purple and Circuit spring to mind as "make anything" styles which also have a distinct and unified theme, and Lab and Honeycomb are probably the closest to feeling like OG styles.
I'll keep looking, there are many styles in the custom archives that I haven't even seen yet.