I see BW having several possible primary settings.
a) The most logical setting is 4 years after DPPt/HGSS. 2010 is 4 years after 2006.
b) The same time period as Generation 1/3 //FRLGRSE. This would be the case if RSE are remade. (Not a new game set in the Houen as I've theorized)
c) A time period in the distant past, which will likely be contemporary with ancient Shinou, the builders of the Shinto ruins, and the feuding nations of Jouto (see Cianwood Island)
etc
I wanted to amend this a little bit, I realized by math was off.
In regards to "a"; BW could be 4 years after DPPtHGSS; and that would be 7 years after RSEFRLG. (Apologies to Ryuutakeshi)
3+ 4=7; for whatever reason I forgot that there are 3 years (game time) between Generations 3 and 4.
[There are 4 years real-time; but because FRLG/RSE replace generation one and DPPtHGSS replace Generation two it's instead 3 years. Everyone get it?]
Option "b" is highly unlikely at this point; mostly because BW are being promoted as a "new beginning" for the series.
No "new beginnings" can exist in a time period we've seen twice in almost 15 years.
Option "c" is still possible as nothing rules it out, but until we have more info what the truth is it's anyone's guess.
tl;dr
BW should be 7 years after RSEFRLG/ 4 years after DPPtHGSS