Something like this might be interesting to encounter as an npc, but I think there are some tricky things to consider if you want to make them playable characters.

Firstly, I don't think the people of Eorzea would treat an Allagan Automaton the same way they treat the playable character. Whatever the playable races are, they need to be something that people would welcome into their guilds and shops and settlements. Secondly, I think a lot of text in the game would need to be changed if your character was a member of this race. For example, anything that refers to our character bleeding or breathing, really anything that has any connection to our being organic beings...which I imagine would be a lot.