[ 2016-11-10, Tim Song comments ]

The "non-operator" seems to have been added at the wrong spot. The problem at issue is permission to call operator functions found via ADL, not permission for operator functions in the standard library to ADL all over the place. The problem is not unique to operator functions in the standard library — a significant portion of <algorithm> and <numeric> uses some operator (==, <, +, *, etc.) that may be picked up via ADL.

There is also an existing problem in that the example makes no sense anyway: the constraint in this paragraph only applies to non-members, yet ostream_iterator::operator= is a member function.