Until ACF builds this in you will need to build conditional logic for specific fields the way that @marlonleite has given in the example.
I’ve been looking at the ACF JS code for conditional logic and here’s the problem with using fields other that choice fields. ACF does not make any AJAX requests here. It simply looks at the fields in the editor. In order to use any other type of field, like taxonomy, relationship, post object or user, ACF would need to make an AJAX request to get the values that it would need to display. I’m guessing that this would be a major change.
As far as builing an add on there isn’t any way to extend the JS code that’s already there. Someone would need to override what is there and replace it with new code. I don’t know if this is possible. If there is anyone here that knows a great deal about JS and jQuery and you can explain how to override existing functions, maybe it would be possible for someone to write an extension for an add on. If your interested the code for conditional logic is located on about line 1500 of /advanced-custom-fields-pro/assets/js/acf-field-group.js
If someone can tell me how to go about overriding those function I might be willing to give it a shot if I can find the time.
I know that this is a long standing request, but Elliot is the only developer, there really isn’t a “Team”. I’m sure that this is on the to do list, it probably just has a lower priority than some of the more important changes that need to be made, like the proper use of term meta which he’s started working on.
