It's unclear whether (extended) APIs will be free to modify the JSON API media type with proprietary parameters.

If this is not going to be allowed, then the newly created Media Type Negotiation section could just as well prescribe a blanket ban on any parameters instead of singling out ext.

But if proprietary parameters will be allowed, then it means JSON API itself won't be able to introduce new parameters in the future without theoretically risking conflict.

Any option between these two extremes seems to require some kind of namespacing scheme, similar to those currently being discussed in #602.