I'd personally prefer that we don't stray too far from the book. I'd also like to keep a few aspects of the book's general style as well:
1. Hybrid cultures (Anglo-Indians, French-Algerians, Chinese-Japanese)
2. Empires that aren't too balkanized (Raj, France-Outremer, Caliphate, Brasil). Maybe they are fractious, with areas outright in revolt, but I like the general idea of the Fall being so bad that only the strongest nations are left in its wake.
3. Huge areas of untamed, wild lands. (North America, Africa, all of the shadowy bits of Latin America and Europe) Because having huge parts of the U.S. survive kind of undermines the entire style of the original novel.
And Soverign in the other thread brought up a vital point: there's a little Ice Age. Huge parts of the world are screwed and destined to fall to cannibalistic chaos.