Spoiler ShowI know and understand his role in the Replica Program, I'm only speaking of Vexen's design, voice, and personality, as well as that awful laugh, but I do get that he's needed for his brilliant mind.
Spoiler ShowWell yeah I don't think there are very many people who would say they particularly like Vexen, but again I'm just looking at who should be in the new Organization XIII based on story (which is the most important thing for any form of media, entertainment, or storytelling.) and also based on what makes sense and based on Xemnas' statement in KH3D on who would qualify from the original Organization to be a part of the True Organization XIII.
In my opinion the roster for the Seekers of Darkness that makes the most sense would look like this:
1. Master Xehanort
3. Ansem Seeker of Darkness
11. Riku-Replica (Brought back by Vexen)
12. Young Xehanort
13. Xion (Brought back by Vexen)
This list fulfills what Xemnas says in KH3D. First he said MOST of the original Organization XIII were unqualified to become vessels. In this list we have 6 of the original members of Organization XIII included, with the other 7 being excluded. (I'm not counting Xion in this equation since Saix flat out says in 358/2 Days she was never a true member of the group) Meaning, like Xemnas says, MOST of the original group is not included in the new group. Second there are no traitors like Marluxia and Larxene, which Xemnas clearly says was a disqualifier for the new group. (Yes I know Xion was a traitor, but if Vexen brings her back they will likely have her Norted right from the beginning this time around).
That being said I do think Marluxia and Larxene are going to end up turning on Xehanort at some point in KH3, and they will be replaced by Riku-Replica/Data-Riku and Xion.