Thanks for investigating this. I also think xforms-ready is meant to fire every time a form is loaded (whether empty or with an existing record).
Enketo doesn't yet support events and actions, so we won't have to consider breaking anything.
The choice between (1) using xforms-ready and (probably) deviating from the W3C spec or (2) inventing a custom first-load event, depends mostly on whether we think the original xforms-ready event could be useful to us in the future. If so, we do not want to deviate and should choose option 2.
At the moment, I cannot yet think of a use case for the official xforms-ready event.