ZNM & KI’s NM:
Do it, you could use FFVI as an inspiration for the storyline, you can probably use something like FFX “Coliseum” where we need to catch monster for a crazy professor from the Garlemald empire, who make nasty experiment to create new monsters with their DNA, you could do that very easily, it would be fun to go out in the open world with your FC to try & catch monsters. That Professor could give you a new bestiary that indicates which monsters needs to be trapped, with a Tier similar to VWNMs.
Of course, each new monster created would drop a new piece of crafting material, and the professor would give you rewards if you can defeat his creations.
Der Richter was a good one too and Crusader from VI as well, you can easily assimilate these and put them into XIV, they would be fun and challenging.