I think most signs point to France. As someone who is from America, I'm apparently obligated to feel some odd hatred to the French, but I don't find myself within that ability. (Somehow, hating one of two world powers that helped the US form seems a bit hypocritical. Moving On...)
I would love to see an Assassin's Creed game:
France ---Around the Napoleonic times, although there is the massive economic fall shortly after Napoleon's failure with the Ruskies.
Germania --Before WWI, I'm not well educated on the history of Germany, so its hard for me to pick a decent timeline w/o making myself look like more of an idiot.
As well, I'd like to see some London thrown in. France and Britain both provide some decent climbing, the Eiffel Tower, Big Ben, etc. But the construction years of major monuments may be an issue, again, I've little to no knowledge of the buildings so I can't comment much.
However, I forsee an issue with proceeding into the future, Assassin's Creed has always been very much knife based, and thats how I like it. I'm unsure how guns will factor in. If AC goes the gun route, it will likely just become a bland I'm-different-really game that will bore me.
Thankfully, AC isn't confined to a linear timeline, and if they want to go back before Renaissance Italy, they can. Please no more Altair though, I could never tie myself to that character.