5.0 Story & Zone speculation.

[Iscah]

While Uriangier and Y'shtola in our shard, but inhabited by the souls of others (Matoya and an as-of-yet unknown character, potentially Louisoix?)

It's an interesting theory, but that's either genuinely Urianger or someone using his archaic speech patterns. ("What sayest thou?" instead of "what say you?")