Nineham's comment remains true: "That many readers should be as surprised as they probably will be [at the historical critical content of commentaries] is a sad reflection on the extent to which all denominations do so little to keep an increasingly educated laity informed about the progress of biblical study."
One might date the passage by its use of the word "progress" in connection with "biblical study." Few really believe that any more. However, it reflects Nineham's purpose in writing an introduction for educated, intellectually curious readers coming to the bible from other fields. This goal also dates the book. Few expect people to be intellectually curious any more. He assumes readers will be attracted to the book's erudition & by their interest in the subject, rather than seeking entertainment.
In this regard, Nineham's introduction is a quite useful tour of basic issues in the critical study of the New Testament, focused on the gospel acribed to Mark.