One upon time, we decided that we can replace opNeg, opCom, etc. and opAdd, opSubtract, etc. by generic names opUnary and opBinary.

Why don't we have a single iteration operator? Can't we just provide the "Reverse" information by some bool argument (or string if you like maybe more functionality in the future) like the other operators?

I'd suppose to make opApply and opApplyReverse aliases to <newOp>!false / <newOp>!"Forward" and <newOp>!true / <newOp>!"Reverse" for compatibility.

The workaround I use:
static pure opApp(bool rev)()
{
  import std.format : format;
  immutable code =
  q{
    int opApply%s(scope int delegate(ref Idcs) dg)
    {
      ... (with %s everywhere something Reverse-generic happens)
    }
  }
  return rev ? code.format("Reverse", ...)
             : code.format("",        ...);
}

mixin(opApp!false);
mixin(opApp!true);