It struck me in responding to Steve that perhaps the reason that groups like BOAC et al, appear to contemporary rock fans as irrelevant or behind the times is likely a result of their notational and performance practice. Perhaps the integration of composer with ensemble in groups like GYBE, Radiohead and Sigur Ros encourages the type of experimentation that such a timbrally fluid entity needs to be cutting edge.
Notating a guitar feedback yelp is possible, but playing it just right and according to the needs of the composition is problematic. We have no real rock music ensemble notation and a record of the recording process that Sigur Ros uses would be a record of experiments (as evinced by their recent interview in TapeOp magazine).
Maybe a valid notation (and not merely a record of experiments) is the next step in the cannibalization of rock?
The acceptance of the rock band as a contemporary music ensemble - is it really deliciously subversive or another ploy to garner audience share with music that couldn't cut it with the classical crowd?
Art rock ensembles can certainly be considered an attempt to not just create a popular avant garde, but to act childish in the face of this current contemporary music gerontocracy. But what really is the difference between experimental/minimalist rock and a band like Godspeed You Black Emperor or Sigur Ros in the end? Has the language of rock really been enhanced by the inclusion of random or polyrhythmic elements and atonal melodic stylings? And in the end, how often is this new complex rock that much different than those horrible Chick Corea records where the entire ensemble played simultaneous and complex modal octaves until they were blue in the face?
For me, song structure, in particular, the placement of dramatic solos, forms the basis of great rock music. If the textural elements become so complex, the integral distortions of the instrumentation can become merely fatiguing rather than an enhancement to the capabilities of the small ensemble.
David Harrington, in a recent interview commented that he doesn't even listen to new music that much anymore; that Radiohead, Sigur Ros, et al are just as interesting because they've incorporated contemporary music stylings into their rock.
And let's face it, you can play practically any random notes on an electric guitar, vaguely on or off the beat, add drums and a repetitious bass and get that impression of uh... kickin' ass.
In fact, some groups, do merely that as their primary working method - algorithmic rock. The real question is there any really interesting music being done with rock band ensembles or is it all an excuse to hide under-rehearsed ensembles and ordinary minimalism by adding drums and bass? I have to admit, I've yet to hear a rock ensemble that is more compelling than recent Tortoise or Sigur Ros records. If the contemporary rock ensemble can't even blow away a few Icelandish 20-somethings I can't imagine the future of the ensemble is much to contemplate.
I will admit to a fondness for early Branca guitar orchestra work, however, but that seems to defy the definition of experimental rock as it was the misuse of gigantic numbers of electric guitars that made his early work so compelling.
And I'd like to mention the work of Daniel Stearns, in particular as a standout, original example of an Ivesian approach to rock music with his combinations of microtonal melodies and bizarre theatrical climaxes.
Why couldn't a rock ensemble, well-rehearsed, with great instrumentalists, and really compelling music, be the model for a contemporary music that actually maintains and grows an audience? I suspect, though, that the temptations to degenerate into silliness, the egocentric mannerisms of the soloists and the nature of the popularity of the ensemble in the marketplace, stale as it is, might make that impossible. The beat and the buck enslaves all, it seems, to mundanity.