Well, as it was revealed in UnionX, Ven wasn't just a means to create the Xblade, Ven is someone from the past yeeted into the present day. Although he didn't appear to remember anything, there could still be secrets locked up in that brain of his. If given enough time, maybe Xehanort would've found a way to crack it.
Similar to that random unexplained scene in KH3 where Xemnas says Marluxia, Demyx, Larxene, and Luxord were sought out again on purpose because they are also from the past. That's why AnsemSoD was looking for "subject X" who was probably Skuld.
There seems to be something Xehanort wanted to know or was looking for, the Xblade just seemed to be a way to expedite that process or make it easier, not sure.
What that "something" is he wanted to know, I'm not sure. Maybe he's just a history nerd and wanted to know the full story about the distant past and the recent past (like his mother for example)