I feel that postmodernism has pierced a hole in the so-called literary canon. The criteria for works prior to that movement will probably not change, but the new forms of the novel, for example, pose a serious question to literary critique.
I would go as far as to say that many contemporary works that we call "novels" go by that name because we have not found a new name to call them. Chilean Roberto Bolaño is a case in point. His works have become an object of cult. However, most of them have rambling plots, unsolved situations, characters that appear from nowhere and disappear without rhyme or reason, and seem to hinge on variations of the same theme. Most of them rely heavily on his Barcelona experience. And yet, having scoffed the criteria of the canon, he has become an intellectual must.
Sooner or later, the canon will have to be revised and adjusted to the new works. This would be a great step toward the advancement of literature. In the same way as prescritive grammar gave way to updated manners of analysis, literature needs a breath of fresh air in respect to what may be called canonic.