Still should've been in BBS even if they do add it in later, imo.We could always see ruins later on, if they are one in the same, since TAV pretty much stuck to what felt like a very small margin of a world (especially a final world). I mean, the place Lingering Sentiment was left and is in KH2FM (if that part is confirmed canon) were clearly different/altered.
Who's to say a revisit doesn't show off a wonderful city of decay and ruin~
BBS has many problems, but I think one of the biggest is that the stakes never feel real, and I think actually seeing ruins from the Old World would've helped that some. Wouldn't fix everything of course, but it'd definitely help. Not to make this a thread about BBS or anything though lol.