The truth is that “adoptable storage” has been around in Android since Marshmallow in 2015. What is adoptable storage? It’s basically a device’s ability to treat internal storage (ROM) and external storage (microSD card) as one. Samsung avoided adopting this approach by trying to justify the move saying this feature was useful in low- to mid-range phones. The Korean phone-maker might have changed its mind.
SamMobile reports that adoptable storage might be included, and enabled, in the next Android Pie update for the Galaxy S9 family and the Galaxy Note9. A leaked firmware seems to indicate that users will be able to format external storage with the intent of using it as extended phone storage. This was discovered on the XDA Developers forum by one particular user.
We know that one of the main selling points of the Note9 is the tremendous amount of data these phones can store. Both internally and externally. It would make sense for Samsung to enable this feature on its other phones, as we are consuming more and more data (and 5G is around the corner), and eating up more and more storage space.
This is, of course, not an official confirmation, but an indication that Samsung might enable the feature in future updates. Until we see it functioning on our phones, treat all of this with the usual dose of skepticism.