This is something I've spent a lot of time considering. The difficulty is deciding why, exactly, LotR deserves a place in the canon. It certainly doesn't do anything new in terms of style. Tolkien's writing is very descriptive, sometimes even beautiful, but when viewed against other authors of the twentieth century, it's anything but innovative.
In terms of innovation of content: while Tolkien's world is amazingly, imaginatively realized, stunningly detailed to the point that it seems incredibly real, he nonetheless takes his themes from the works he loved most - the folklore, mythology, and epics of ancient Germanic tradition. Gandalf and the name of every single dwarf in The Hobbit, as everyone knows, comes from the Eddas. I can just imagine the glee with which Tolkien originally used that name, way back when...it was probably similar (and some may feel this is blasphemy...) to the way I feel when I write some of my fan fiction (for an interesting comparison of the traditions of folklore and modern fan fiction, check out this article: http://slate.msn.com/Features/fanfic/fanfic.asp ).
Tolkien's work, in terms of literary classification, is a profound example of nostalgia - perhaps the most nostalgic work of all time. But this alone is probably not enough to bring him into the canon.
Where Tolkien broke new ground in literary history (and this is not my theory originally, it was proposed to me by a Cambridge medievalist and Tolkien fan, but I personally subscribe to it) is the very thing for which this message board - and the newsgroups, and the Tolkien encylopedias, and the endless HoME books, and the Great Debates, and self-made Tolkien scholars such as Mr. Martinez - stand. Tolkien gave us the first work of fiction which can serve as a doorway of research to the casual reader. In its amazing historical complexity, LotR is a fictional work that need not stand merely on its own, nor merely on the literary traditions from which it stems; it allows for *internal* story research, not just external comparisons. What I mean is this: when I wrote papers on Tolkien for a college class, I wrote on Gandalf as an archetype of the Wise Old Man, and also examined the Silmarillion under the theories advanced by Tolkien himself in his essay "On Fairy Stories." These were external examinations of the text. But one could easily write an essay relating the development of a First Age historical event being transformed into a song in LotR. That's a rather quick example, but even such things as trying to decide whether the Balrog had wings, simply from Tolkien's writings, is the same type of thing.
The only other story I've read that tries something similar - and this is in my admittedly limited experience - is A.S. Byatt's "Possession," which invents two 19th-century authors and then devises an entire canon of literature from each within the fictional world of the novel.
But will Tolkien be read in high school classes a hundred years from now? It's difficult to say. Nostalgic works often get lost in the shuffle, especially when sweeping new literary or artistic movements arrive. There's been little in the way of that since Modernism. The miasma of critical theories and smaller movements since Modernism have all been lumped under postmodernism for the most part, and I'm not sure if a new movement will ever catch fire again.
But I digress...as technology becomes ever more omnipresent, I suspect that Tolkien's works will actually increase in appeal. I personally find it the height of irony that Mr. Jackson feels that "now is the time" to produce Tolkien's works because the technology is available...it's almost the antithesis of what Tolkien was doing in writing LotR. Movies can open the door to imagination, but I also feel they can limit it. The Balrog, no matter how it looks on screen, will always be infinitely more ominous and even scary in the pages of a book.
So, between a growing nostalgia and a generation of Tolkien fans gaining control of the literary establishment, I suspect JRRT may indeed find a place in the canon - at least for a while. Of course, having a place in the canon, even for some of the greatest authors - and given the extreme nostalgia of the work and Tolkien's irrevocable, if unfortunate, association with the bookstore-genre of fantasy, he will probably be quite subject to being in and out of vogue.
This is only a small part of my analysis of the idea, but I'm very curious as to others' feelings on the matter.