I didn't play FFXI, but I've looked into the gear/clothing sets that you've described and think that it'd be a great idea. Personally, I'd prefer to see it as a craftable option, and those races that don't have an FFXI representation (Au Ra, male Miqo'te, female Roegadyn, and any others) could receive a little bit of art and design dedication.

XI veterans will probably have a bit weightier opinions than my own, but I think the aesthetic would carry over super well to FFXIV and Eorzea. An homage to XI design that would fit in extremely well!