I know that Daichi Hiroi handwaved the answer here, but there are only a few viable, unexplored worlds left (four, in fact). His answer through Y'shtola sounds rather odd, coming from the perspective of a fellow shard nerd, given that we should eventually have enough clues to map out which remaining worlds are which. Not knowing the answer now doesn't negate the curiosity and desire to discover the answer.

One thing that bothers me is that while partially destroyed shards make for more convenient short story arcs (like Hiroi's grand attempt at an Ultima Thule style finale), you permanently discard the storytelling potential that an intact shard might offer (both in terms of landmass and in terms of accessing inaccessible areas through dimensional travel between two intact shards.) I hope they leave at least a couple fully intact to build future storylines off of.