Flexible screen wont do the stylus inking or poking or hold up very well unless the material gets a lot better.
Bezel/hinge can always get smaller and less intrusive, but there will always be the fold line of a flexible single screen.
agree about materials. Technology is not mature enough right now but in future with foldable gorilla glass it will get lot better.
I believe dual screen devices specially on a smartphone form factor are more of a stop gap solution untill flexible screens becomes mature with durability of screen tech.
I don't think fold line or crease hampers experience as much as bazel hinge.
As much as I like surface duo I don't think dual screen category specially on a smartphone form factor will survive against flexible screen devices after 2 or 3 years when the trend becomes mainstream.
I believe once flexible screen tech becomes mature Microsoft will also adopt it for surface duo.