Great work with V5! I was considering moving away from ACF due to performance previously experienced with large field groups, I believe this was due to double lookups against the fields in the database (Which Local-JSON solves!! Yay).
My only concern is that the fields are saved in the database when local-JSON is being used, I understand this is so that the fields can be edited afterwards however I would love it if the following could potentially happen: if ACF detects local-json is in place, then add a tick box on field creation which would disable saving to the database (Obviously there would be no need for this box if Local-JSON is not in place).
Not going to pretend to understand ACF’s inner-workings, however it looks like this may be difficult to achieve as ACF stores the fields and then gets them through acf_get_fields() for export. It would need to go off of the inputted data as opposed to storing and retrieving – i’m guessing there are a lot of procedures the data goes through which could potentially be missed…