Rationale (April, 2013):

CWG saw no problems with the example. It did note, however, that the assignment to x is not an initialization, so x would not be considered to have been initialized by this example.

There appears to be no prohibition of assignments in member initializer expressions (neither mem-initializers nor brace-or-equal-initializers):

  struct A {
    int x;
    int y = x = 37;
  };

This seems surprising. Should it be allowed?