As in if they're on the iPad, in the Photos app, I want to move the files to Photos on the Mac, along with the edit information made on the iPad, but I don't want the files stored on the Mac inside the Photos.app managed library, I want them stored on disk in date-hierarchical sub-folders, and accessed as referenced files within Photos.
Is there any reason why you want to use the Photos app on either side in the first place? Besides convenience?
You could use
RAWPower and manage your images completely in Apple Files (creating the folder structure you want/mirror to the Mac).
RAWPower on iOS provides
Copy to RAW Power - an extension added to RAW Power 3.0 for iOS. It works by integrating with the Share menu in iOS apps. If you use that extension to share an image to RAW Power, then that image will be saved in the Files.app storage container for RAW Power (not in the Photos library). If you share a single image, then RAW Power will open that image into the RAW Power editor. If you share multiple images, then the app will display the thumbnail grid.
So Can Photos on the Mac import from an iPad's photo library, but store the images as Referenced images (I believe it can with a normal camera / card import), and can it do that when it's importing photos that have non-destructive versioned edits etc.
Due to the fact that you can have all images and edits reside in Apple’s Files storage container you can just copy it to e.g. an external SSD and use that to transfer them and their folder structure to the Mac.
I highly recommend to use
FileBrowser Pro to copy the files from the iPad to the external storage.
Apple’s Files app is prone to introduce errors into file systems which can result in damage files. File Browser additionally allows to share files and folders from the Apple Files storage container and/or connect from the iPad to a shared folder on the Mac when you connect both devices by ethernet cable or per Bluetooth or WiFi.
Because RAWPower runs on MacOS too you might be able to use the the non-destructive edits you transferred. You have to check for yourself - RAWPower offers a free trial - or you check with
Nik Bhatt its programmer. He is really, really helpful.
Does transferring the edit states preclude the use of a referenced library... I know referenced libraries don't work properly with iCloud library, but that's no loss to me, because i'm looking for offline solutions.
A Photos based solution will probably not work - that is because, when you adjust e.g. a RAW image on iOS and save it back to the system photo library, the editing app provides iOS with a full-size JPEG. By doing this, other apps can use the adjusted image without knowing how it was made.
I haven't tried any of this, I'm just looking for ideas as to whether something is possible, or if anyone has tried it.
Pixelmator Photo together with
Pixelmator Pro might offer a similar solution. Pixelmator Photo allows to edit, save (incl. the non-dwstructive edits) and manage images within the Files storage container too. No clue wether Pixelmator Pro on the Mac side can use these in a meaningfull way though.
That is one of the main problems - wether for RAWPower or the PP-combo - meaningfull use of the non-destructive edits with out automatic sync within the designed environment.
As far as I know it does work only via the frameworks Apple provides - and the iPad side sets the limits here.
Yes, you can e.g. easily export, copy, import presets or LUTs into RAWPower between iPad and Mac - but the whole scenario seems filled with tedious manual tasks, impacted by e.g. the file system restrictions on iPadOS (for example if you use a dual USB-Stick to transfer your images from the iPad, iPadOS doesn’t offer a function to check how much space is available on it nor does the copy function. iPadOS will start copying and if it runs out of space on the target it throws an error. Might be improved in iPadOS 16 😎).
IMHO the whole thing you want to implement seems like it will be at least a master class in staying concentrated regarding the workflow (default target is the Photos library… a moment of lack of concentration and you might work with and on files in it again 😃) and live with some - maybe even tedious - workarounds - but it might be acchievable. 😀
nota bene: I do almost all developing and editing of the RAWs I take on iPPs.
And the functionality provided by the current available apps does what I need for my semi- and professional photos (the latter being stitched, focus stacked or other forms of micrographs).
And it can even be fun to do cross platform edits and management when you embrace the functionality provided by the systems.
Working with files with in the iPadOS Files storage container is not. Even if FileBrowser Professional keeps you largely covered.