Hrm. I guess that would depend on how quickly things were going to be published. Personally, I like something I can start playing with quickly. A perfect example would be the Forgotten Realms pack. It had a couple of nice maps with a large overview and major place names. Then, in the books, it detailed out a few key areas. Just enough to basically start playing in while waiting for the next installment. I think that a lot of it will have to do with how many changes you might be making to the gaming system in use. If, for instance, it is the latest version of ADnD, you can probably expect most players to be familiar with the rules, thus, you might detail out whatever changes there are in a DMs section, and so on.

It's kind of a tricky question because everyone has different levels of desire when they pick up a setting/source book. Since shifting over to Hero Systems several years ago, I've come to like their style of source material, but I'm not sure that's applicable in this case. If it were me, I'd focus on making sure that in the first book, there was enough to start playing with in short order, and that would depend on what the minimum detail is to start adventuring in the setting.

Honestly, though, I wish I had a standard answer for you on this one. (Head scratching). Of the options you listed, I think I would tend towards the last option.

Or would you want a world overview, 1 or 2 nations covered in extreme detail for each time period, and some promise expansion of details for the rest?
For me, I think that would be enough to start playing with and, assuming I liked the setting and any applicable rules adjustments, I'd probably wait for more in eager anticipation. Though you might not need to go into "extreme" detail. Just enough to give a solid feel for the setting and still leave room for creativity. You could always add in more detail with supplements if the setting becomes popular enough.

Hope that helps.