What I’ve always wished is that I could take pictures with a nice DLSR or bridge camera and have a way to quickly load the RAWs into my phone for culling and processing.

Apple makes (made?) an SD Card to lightning dongle. It's a wonderful thing on vacations.

I can take the SD Card from my Hasselblad and plug it into my iPhone. I then delete photos and videos I don't want, upload the keepers to iCloud as a backup, and AirDrop pictures to my wife so she can send them to her friends.

iOS has no problem with most current raw formats, and you can even convert them to JPEGs right in the phone.

You can also import the raw images and do basic editing of the photos with the Photos app.

The only problem I've run into is with long videos sometimes being laggy. But that might be an issue with a slow card, or moving data over a Lightning interface.