Deep Space and Disney Town don't have a POH living in their world and they are still in BBS.
Not all the worlds have to have POH.
Atlantica makes sence because it will explain the reason Triton hates keyblade wielders and Atlantica has so much back story. BTW, OC means Olympus Coliseum, dah
You have some goods points there but I'm pretty sure that when KH1 was made there was no thought about BBS. Not saying there wasn't though because the Riku vs. Roxas fight is the secret video and that wasn't fully explained until the end of Days. So maybe Atlantica will be in it.