Double-faced cards, though they may have just been a mechanical reworking of the earlier flip cards of Kamigawa block, were the mechanic of Innistrad block that made the greatest splash. Initially divisive, transform cards proved to be an almost unqualified hit. But for a lot of logistical reasons (expensive to print, have to include the checklist card, have to sort them special in booster packs), they have yet to be used again. Of course, Innistrad's feel was perfect for them, so any block whose flavor also worked as well for transform would be likely to get it. Now, Lorwyn/Shadowmoor block's overarching story involved the Great Aurora, an event which turned the plane from eternal daytime and optimism to eternal night and terrifying gloom - hmmmm, aren't the transform card face symbols a sun and moon? Mark Rosewater addressed this idea recently on his Tumblr blog.
When mikekraemer asked, "Do you think it would be cool to see double-faced cards and transform return in block set on Lorwyn/Shadowmoor?"
There are many cool things we can do with double-faced cards.
This is an oblique response, to be sure; the relative unpopularity of Lorwyn makes a return to that setting relatively unlikely, at least in a regular set release, and double-faced cards are probably not supplemental product material thanks to smaller print runs not justifying the expense. Still, the flavor is an absolute perfect match. Some individuals from Lorwyn were represented as their changed selves during the Shadowmoor mini-block, but to really get the flavor of the Aurora's changes across both versions should be represented on the same card.