My order:
KH BBS > KH2 > KH 365/2 -> KH1
*CoM is missing because I never played it more than 30 mins even though I own it in 2d & 3d!
*I think KH1 level design and combat is poop so even though 365/2 is zzz repetition, at least the combat is awesome and OMG I LOVE ROXAS HE IS SO CUTE AND EMO AND I WANT TO HUGGLE HIM ALL DAY

**and Roxas has a better theme song than Sora
Anyhow I talked to duckroll about this and we pretty much agreed what is happening is there is one game concept at this point to finish the KH franchise "or as Nomura calls it the Xenohart Saga".
This game is going to take place 50% in the old worlds & 50% in all new worlds
We think Nomura is splitting the game into 2 parts. The 3DS game by the Osaka team (BBS team) will be like Matrix 2/LoTR2 where it will be the first half of the movie, cover the old world revisits and end on a cliffhanger in 2012 and hype up KINGDOM HEARTS III which will be the 2nd half and final conclusion to everything in 2013 by the main KH Tokyo team.
At least that's my prediction. Storywise this will make sense after you guys finish BBS.