You could probably handle the one catch per area (if a player's captured pokemon is from an area, disable balls in that area, or something along those lines - then disable releasing pokemon, and have a dedicated death box) and nickname rules too, although it may not be desirable to do the latter. Dupes clause could probably be enforced in a similar way to one catch per area. Still nothing stopping a player from resetting if something goes wrong though.
Honestly though, just having one single "Nuzlocke mode" is either too restrictive or does too little to be worthwhile. Too many var