To answer one of your questions, creating a text field for the upload path was one of the setting I thought about when I replied. Honestly, I don’t know the specifics.
In the upload pr-filter, I think I posted this somewhere in the past acf/upload_prefilter the field ID that the image is being uploaded for is in either the $_GET or $_POST array, I don’t remember which and I don’t remember the array index without testing. In addition to this I believe the object type and ID is also amongst the data available in the request. This value can be used to get the field object that includes any custom settings.
I don’ know if you want to do this with field settings or you want to figure out how to do it automatically for every image field. Field settings would give you some configuration ability.
Of course I don’t have the details on doing any of this. It would be a rather large project to investigate the options and I don’t currently have the….. resources to do so. Just throwing ideas out there base on some of the work I’ve done with altering upload paths.
