Ava,
Adele,
Adeline, and
Adelaide seem to have made a comeback, so I think it's likely
Ada could too. It's probably already not that unusual as a NN for
Adelaide,
Adeline, and Addison...at least in the US.
I don't dislike it, but I don't particularly like it either. I'd rather see something even more old-fashioned, like
Ida or
Adair.
This message was edited 3/29/2016, 7:55 PM