It only concerns file format right? I interpreted the preceding conversation as talking about format in the sense of data having the same schema and maybe being interoperable, and not just file format. Nothing I read seems to indicate that seamless interoperability is a requirement [0] [1].
Interoperability seems a little difficult to enforce, like brokers that don't support fractional shares might need to start supporting them to import data from other brokers. Edit: I guess this example is poor but I just wanted to point out that schema/interop also involves data domain, validation, etc.
