What is a canonization and why should we want it? At first glance it seems like positing a single album, or a set of albums, as the definition of a certain style, would be a bad move, relegating all other albums to a sort of in-between status of imperfect imitations. It would be to say, so the objection goes, that these other albums were derivative and subpar, when really we should want a democracy of values arranged (of course) non-hierarchically.
I would suggest that, on the contrary, canonizations can at their best function as an index of events (I at least want to say this is true within the extreme metal world, I'm not sure about the specificities of other domains). In this way, being minimalist in our claims and having a macroscopic view of the domain as a whole, we can look back and say for certain with musical moments were eruptions of the new and which were created upon the implications of that newness. These other bands/albums/whatever would not be "derivative" in some typical sense, since they would be creating in fidelity to that earlier event, would be focused on expanding that event with an eye towards completion. Music created in the name of these events could of course be of varying qualities, but which of those pushes the genre along and which are content to stagnate - this is another important question. If the event opens a space of possibility (speaking somewhat loosely here), the postevental fidelities work through the possibilities and cannot be content to stop. Also, of course, a genre may become saturated, which requires a new event.
All this so far is what I understand from Badiou. I am of course applying it on a more micro-level than I have seen him do - I look not at "music" (his favorite example of a musical event is Schoenberg) but at "extreme metal" or even smaller subcategories like "black metal" and its niches. I think, however, that the theory applies on a multitude of levels, since clearly not all events are equally realized, equally "important" or "influential", equally "large", etc. But they are all events - I think this flexibility is what makes Badiou's theory so powerful, and once learning some of it I couldn't help but begin to see the same structure everywhere, but especially in extreme metal, based as it is on insane fidelity (I'm a metalhead myself, I should know!). Also: This is only my interpretation of Badiou, which I may end up deciding is incorrect after further reading.
In any case, proposing canonizations is harder for larger genres (of course). I may attempt some smaller genres: Blasphemy's Fallen Angel of Doom... (and the demo? These discrete outputs make it a little hard to say) for bestial black metal, Conqueror's War Cult Supremacy for war metal of course, maybe Suffocation's Effigy of the Forgotten for brutal death metal (but a case could also be made for including Disgorge's early albums), Devourment's Molesting the Decapitated for slam (though the style was purified and first presented in its slam-without-death-metal form by Cephalotripsy's Uterovaginal Insertion of Extirpated Anomalies).
This already presents a problematization of the claim that canonization tracks events - Devourment clearly opened the way for slam, but at that time it was only a possbility. Devourment as event was a newness - Cephalotripsy was the most utterly faithful to that possibility of newness that it cast aside all that was old in Devourment (namely, death metal). So what should a canonization provide? Perhaps both event and full fruition. Sometimes these are the same however - Deathspell Omega's trilogy, but especially Paracletus comes to mind, that masterpiece of an album. What are the results of Paracletus? Who has the courage to have faith in it? Dodecahedron, maybe. The point is simply this: there are a number of possibilities, and due to the complexity of modern music production the field is pretty messy.
Question: Has every style found its full expression? Maybe every nameable one has! Full expression seems oftentimes to coincide with nameability. New elements may yet exist in music being produced today which we cannot yet separate and form into a coherent style - this is just the nature of the event, an ephemerality undecidable from within.
A better question: why haven't more people been doing Badiouian music studies?