FWIW, I would presume the reason that was added would be some shortcoming(s) in [1], since I doubt they wrote a minifilter driver just for kicks.

(It might have been that some programs were doing IO that avoided triggering the change notification, and a sufficiently large {number of customers,customer} complained about it.)

I don't work for Dropbox, and I haven't used the API, but as I said, I really doubt they added a (signed) driver requirement lightly.

[1] - https://msdn.microsoft.com/en-us/library/aa364417%28VS.85%29...