Modern times would be sweet but I would be cool with Feudal Japan, Boxer Rebellion China, or my favorite the French Revolution.  As Marie Antoinette once said "Let them eat golden space apples".

I think that would be the only setting they could use which would cause me to NOT buy the next game.  Desmond has less character than a brick, and all that Animus garbage is utterly pointless.  It literally boggles my mind that Ubisoft created these lush, interesting game worlds like the franchises depictions of Rome, Jerusalem, Florence etc and then felt the need to add a layer of sub-Matrix derivative sci-fi clap-trap over the top.  

Maybe the next AC could be like a closer relative to Desmond, like how he ended up to be American(?) or British(?)(Really don't know what nationality he is). 
I definitely don't want a modern day one, because that means three things; machine guns; action and CoD styled action even though its a stealth/parkour game, it would be best if it was kept in the past.

" that means three things; machine guns; action and CoD styled action even though its a stealth/parkour game, it would be best if it was kept in the past. "

It would be a huge mistake to jump from the 1100s, to the 1400s, to 2012.  The span of time outside of the Animus that AC, AC2 and Brotherhood took place in was a few weeks according to Brotherhood, and they have more than that amount of time before things start to get uh...heavy.  Also, without spoiling anything, the story doesn't seem to be anywhere near a conclusion and is just getting more and more interesting with each installment.  I think were about 2-3 time periods away (I don't want to say 2-3 games away, since they could always spin off a future episode just like they did AC2) from the Desmond entry of the series.  And hey, who knows, maybe there will still be more in the story after that.