That's certainly not true. Interoperability for basic features such as text, photos, videos, posts and comments doesn't mean apps are not free to add more features. Also, having an extendable framework will easily account for this
some form of interoperability is already happening for some of those data types (or at least starting with portability). See the Data Transfer Initiative (dti.org)
The issue is that forced interoperability will lead to platforms creating an interoperable (and less fully-featured) version of their app to suit the regulations.
I do think that interop is important, but I think it is a harder problem than most people think.
