Would it be possible to implement the mirror source provided by the FSL3 modded app as in first juggluco solution as data source? With that there would not be a need to root the phone and at the same time you'll get all the freethree benefits including the clever gadgetbridge support.
Yes and no. It would be possible, but not that easy. First, the logic for the Gadgetbridge support resides in the module loaded with the Libre 3 app, not the Free Three app. So that would need to be migrated and generalized (which must happen for the G7 support anyway). Second, you'd lose quite some information as far as I know, e.g. the trend value.
But I guess it would be possible, yes.