Reviewing some old interviews, I came across this:
"Gemaga and Dengeki PS Magazines (2007)
Gemaga: Are the characters who appear in the new CG “secret movie” added to Final Mix from the new title?
Nomura: They are people who have some relation to the new series. However, the next title won’t just be Kingdom Hearts III. If it were III, we wouldn’t call it a new series.
Gemaga: Will Sora and Riku make an appearance in the new game?
Nomura: *Laughs* I can’t say. It may have something to do with Xehanort though.
Dengeki PS: What can you tell us about the new title?
Nomura: First, it’s not Kingdom Hearts III. Of course, because we’re calling it a ‘new’ series, it won’t be Kingdom Hearts III. Also, it’s a series, so it probably won’t be just one title."
This is from 2007, after II Final Mix +'s secret video about BBS.
proof he's talking about BBS:
*snip*
s “Aqua” and “Ven”. Are those the names of the other 2?
Nomura: Yes. The blue-haired girl is Aqua."
source: Summary of Kingdom Hearts Interviews - Kingdom Hearts 3
tl;dr: 2007 rumor on BBSV2
"Gemaga and Dengeki PS Magazines (2007)
Gemaga: Are the characters who appear in the new CG “secret movie” added to Final Mix from the new title?
Nomura: They are people who have some relation to the new series. However, the next title won’t just be Kingdom Hearts III. If it were III, we wouldn’t call it a new series.
Gemaga: Will Sora and Riku make an appearance in the new game?
Nomura: *Laughs* I can’t say. It may have something to do with Xehanort though.
Dengeki PS: What can you tell us about the new title?
Nomura: First, it’s not Kingdom Hearts III. Of course, because we’re calling it a ‘new’ series, it won’t be Kingdom Hearts III. Also, it’s a series, so it probably won’t be just one title."
This is from 2007, after II Final Mix +'s secret video about BBS.
proof he's talking about BBS:
*snip*
s “Aqua” and “Ven”. Are those the names of the other 2?
Nomura: Yes. The blue-haired girl is Aqua."
source: Summary of Kingdom Hearts Interviews - Kingdom Hearts 3
tl;dr: 2007 rumor on BBSV2